**BEFORE**

Looks like a pre-schooler finger paint project.

In this write up, I share the research, tips, and process I used to re-caulk our Trekko. I am classifying this as a mod, instead of general maintenance, because it is upgrading and improving the caulking typically used. This guide is meant to be beginner-friendly too, if you’ve done caulking in your shower, you can do it for your EKKO too!

This guide specifically applies to caulking the side-wall components and joints. Roof and undercarriage sealing should be considered separate activities from this guide.

Knowledge Disclaimer: The guidance in this post is backed by my three years of chemistry education, five years of aerospace manufacturing experience, and professional guidance provided to me by a certified RV tech and a family member who professionally did RV restorations. It is always advisable to seek the consultation of an RV professional if you are not sure about how to do things!

What Are Most EKKO Exteriors Caulked With?

If you look at the caulking on your garage doors, panels, lights, joints, etc., it is Henry 212, a type of thermoplastic sealant. This is a general purpose sealant that meets minimum requirements for filling gaps, offering strength against road vibration, and permitting expansion from temperature fluctuations. However, thermoplastic sealants are not meant to provide long-term durability in the face of constant environmental and road stresses that our EKKOs go through.

The Exceptions: Window Sealants and Model Years 2025 Onward

In my research, I reviewed the Winnebago sealant specifications sheet to understand what sealants were used and where to apply them. Window sealants on our rigs use SikaLastomer-714, a type of sealant that is applied to the interior seal of windows during install at the factory. This means that windows do not require additional exterior sealant and should be excluded from this mod project. However, it is still advisable to regularly inspect for gaps to prevent delamination in your side paneling.

Interestingly, I discovered that Winnebago changed to using SikaLastomer-714 for all exterior components on the following implementation dates:

Compartment Doors: 11/6/24

Feature Trim: 12/11/24

All Side Wall Components: 1/13/25

If you have a model that was built prior to these dates… then sorry! You have to join the exterior caulking club!

What to Use Instead? Non-Leveling Polyurethane Sealants

So, what do the experts suggest we use to seal our EKKOs? I was instructed to use polyurethane sealants, specifically non-leveling ones (these simply means it is thick and won’t run messy when you work with it). Some examples suggested to me included Geocel Proflex RV and Sikaflex 221.

Below are some details on the benefits of polyurethane sealants:

Roof Seams - Chemically bonds; stays elastic through temperature swings
Windows & Skylights - Bonds to glass, metal, plastic; paintable; stays flexible under vibration
Wall & Roof Accessories (vents, ladders, solar mounts) - Acts as adhesive + seal; handles vibration, driving stress, and load
Undercarriage & Exterior Trim - Resistant to water, diluted acids, oils, road spray; durable in harsh conditions
Flexibility - High elongation (~500%); remains rubbery
Durability - Long-term, UV and weather resistant
Paintable? - ✅ Yes
Color Options - White, gray, black
Best Use - Long-lasting, structural, watertight RV sealing
Re-Application Possible? - Yes, forms new bond to existing sealant

For this project I chose to go with Sikaflex 221 in white for most joints and used black for larger coach-cab fill gaps and roof corner gap applications.

Project Tools

Metal paint scraper (this is for manually digging into cracks to pull out sealant)

Plastic, disposable razor blades (for manually scraping excess caulk off sides without scratching fiberglass), I recommend two packs
Painter rags
Acrysol (an autobody-safe solvent that is safe to use on painted-surfaces and plastics, this is a Ford OEM-approved solvent which is why I went with it), I recommend 2 quarts
Caulk gun, if you can afford a battery-powered one I highly recommend it to reduce stress on your hand joints
1 inch wide blue tape, I recommend 2-3 rolls
Sikaflex 221 sealant, I used 3 tubes of white and 1 of black for this project
Nitrile gloves, I recommend a giant box from Costco, you will be changing gloves A LOT
Ladder, minimum 8 foot
Step Ladder, minimum 3-step
Pliers
Knee cushion pad
Step stool

Process

This project took me 20-25 hours. This project is extremely laborious because you have to mechanical (by-hand) remove the Henry 212 from the joints and seams. I did try to use a few other solvents/tricks recommended online (citra-safe, WD-40), but did not find great success with them when removing the Henry 212 thermoplastic sealant.

I HIGHLY suggest the use of blue tape to ensure even and consistent lines. The Sikaflex 221 instructions suggest the use of blue tape too. This ensures that the new sealant is pushed into joints/gaps and doesn’t get smeared. If you don’t want your caulking looking like the existing pre-school finger paint that is on your rig, you will need to spend the time properly taping. It’s brutal, but worth it!

Below is a quick summary of how I approached each section:

Garage Doors, Lights, Vents, Sensors, Plugs

Use a metal scraper to push into gaps to pull out tail segments of sealant, if possible, pinch and pull out sealant

Note: You must ensure that you actually get all the existing sealant out of the gaps

Use a plastic scraper to shave off excess caulk around edges on fiberglass
Take a rag and put a generous pour of Acrysol on it, then go around the edges to “buff” out the existing sealant around edges and on door edges, this will require lots of elbow grease
After the Acrysol dries, take blue tape and create a thin border around the gap edging

Note: For the bottom of doors, you want to leave a 2-3 inch gap to allow for proper water escapement

5. Wear nitrile gloves, then apply Sikaflex 221 onto the gap between the blue tape boarders

6. Use a *gloved* finger to push the sealant into the gaps, this will also even out the caulk surface

7. Remove your sticky gloves, or replace, and then slowly pull tape off

8. You should be left with a nice line around your doors

If your lines come out with excess sealant, or you get excess on the door seams, wait 20 or so minutes until the caulk is tacky, and then take a little Acrysol on a rag to clean it up.

Non-leveling sealants are THICK and can be hard to work with. I recommend that you break your work up into 2-3 hour sessions over multiple days. This will ensure that your joints, muscles, back, and hands get a rest break between sessions. Utilize proper ergonomic tools (ladder, step ladder, knee pad, stool) to help you improve posture during this work.

Coach-Cab Gaps

When inspecting my rig, I found a significant amount of caulk had been used to fill around the gaps between the coach and cab. Some of this caulk was up to an inch thick in some places, and I had some gaps a ½ inch wide that had never been properly sealed. I highly encourage owners to check these areas thoroughly. These problem areas didn’t present themselves during our walkthrough a year ago, they came to exist during our first year of ownership, so again, my advice is to keep on top of your sealant inspections!

Pliers are going to be the best tool for pulling these large chunks of caulk out. I started with the metal scraper to pinch out a section and then used pliers to pull the remainder. Your results will vary, but you might have to get creative with how you pull these chunks out.

I used black caulk here because it blends in well with the surrounding black paneling.

Roof Corner Gaps

I was advised by a certified RV tech to seal around the upper corners of the roof, especially near areas where there is significant, potential water runoff from gutters and the top of the roof. Since our rig is parked on a slope, a lot of water makes contact with the passenger-side back corner, so I took extra precaution to caulk this corner joint.

Other Areas

You may find other areas that you have to caulk for this project, so do a thorough inspection utilizing the Winnebago caulk specifications sheet. For instance, I discovered that Winnebago had not caulked the top of our entry door or gaps in the backup camera wires. While discovering these quality issues is frustrating, the lesson here is to make sure you do a check of your sealants on a routine basis!

Maintenance Mode

If you followed this guide, then you should be able to get many, many years from your polyurethane sealant.

You should be able to successfully re-apply polyurethane caulking on top of itself due to its self-bonding properties (yay, chemistry!).

Occasionally inspect your seals, if you find that there is an area that needs re-application, you should:

Clean the area with Acrosyl
Mechanically remove small sections that have worn down from environmental stresses, these will look color changed or not adhering to the surface in which you applied it
Blue tape the area
Re-apply sealant over the top of existing sealant that is still in good shape

Caulking Your EKKO