4500 Trillium Floor Repair/replace

[Island Claire]

I have been stalling on this as I know it could be a big job.



There is a soft spot on the floor in front of the rear dinette, and the floor under the fridge is coming apart.


The previous owner, the one before the one we bought it from, had a shower inside, but I do not know the set up, I was only told about it. It had been removed before we bought it.


The trailer is water tight - all windows and roof vent have been redone and the wood replaced, and the belly band has been removed and re-fiberglassed.


So, do we replace the whole main area? Do we just do the one spot?


Is the plywood adhered to the fiberglass frame and floor?



All the pictures I can find are people who have had a rotten floor that disintegrated. We are not there yet, except for a bit under the fridge.


Please advise as to what you would do

[David Tilston]

Claire, I have put much thought into this question, long before you asked it. What I am about to say is strictly speculation.
It would make sense for the plywood in the floor to be bonded to both the fibreglass that covers the top and the bottom of it. You would be further ahead if the plywood had disintegrated. That way you would not have to worry about getting it out.

The quick and dirty solution is to cut a sheet of ½" plywood to cover your floor. That will spread out the stress so that the soft spot will not be as noticeable. Put a carpet over the plywood and enjoy your camper.

As the soft spot grows, and becomes a problem, in my opinion, the best approach would be to remove the coach from the frame, and cut off the bottom, from the outside. This makes it un-necessary to butcher the furniture inside the trailer. I would cut along the bottom of the, “pontoons” from where your front dinette exposes the plywood to the wheel well and around where the inside of the wheel well to where it meets the rise in the floor to the rear dinette floor level. That should be where that piece of plywood ends. If the bottom of the trailer doesn’t just fall off at this point, then some of the plywood is still intact and still glued to both the top and bottom. This is where I run out of ideas. I was thinking a long rope saw, but my short search for one came up with a maximum length of 48”, (https://www.amazon.com/dp/B0878282DR). This may be long enough, maybe not. A long wood blade on a reciprocating saw might help, but if the intact wood is in the middle of the cut section, then it may be necessary to cut smaller pieces. In the end this butchery would be on the bottom of the trailer, and not seen by most people.

Once the rotten plywood is removed, I would replace it with 1” thick, pultruded grating, (https://www.grainger.ca/en/product/I...FT-/p/WWG4AUC3). It is expensive, and ¼” too thick, but it would never rot again.

[Island Claire]

Hi David, and thank you. I value your input as I know it comes from a vast knowledge base.


Someone one the trailer group posted the following with agrees with what you said.



"the floor is two fiberglass shells connected together. The upper fiberglass has no plywood and the lower fiberglass is a sandwich with layer of resin and glass on both sides of plywood. 2. How far into the cupboards does the plywood go? All the way to outside walls except not where wheel wells are.
3. Is the plywood adhered to the fiberglass outer shell? It is integrated into the middle of the bottom shell fiberglass."


This was based on having to redo the floor as it was completely rotten.


My husband and I had pretty much decided that we would remove the rotten wood under the fridge and replace it with well fiberglassed plywood and possibly replace the soft spot, and then leave it at that.


Your idea of placing a new floor on top is a good one. And I think we will go that route.

[thrifty bill]

The Trillium design makes floor rot much less common. But it also makes repair much harder.

Somewhat interesting, when I was looking for a vintage Trillium, the first two trailers I found both had rotted floors. Both were 4509 models. I passed and bought a 1300 instead. One was a real heart breaker, as it had the factory roof air.

The classic was the one David bought with the collapsed roof and full of snow. Yet the floor was still good! Incredible!

[Island Claire]

Thought I would update this thread.


We carefully opened up the top layer of the floor to have a look underneath, as it did not feel like it was attached. We were correct on that.


there was a layer of gel coat on top of a layer of fiberglass/resin mat and then the plywood.



the only rot was in the area where the original mold gap existed. We coated that area in rot stop and left it at that as it was still intact and fairly solid in consistency.



the lifting of the gel coat and was caused by a large bubble in the mat. The factory had put screws into the gel coat to pull it to the plywood, instead of sanding the original bubble.


One interesting thing we did discover was that, contrary to popular belief, the floor is not one solid sheet. There was a join in the plywood that ran from the edge of the fridge to the edge of the closet by the door.


We relayed fiberglass mat and then used short thread fiberglass to re-level the floor, and some bondo at the end to do the small bits.


Now we are going to lay vinyl plank.

[David Tilston]

Thanks for the update. I am a bit surprised that the inside floor was not attached to the plywood. I would have glued them together. This makes my plan to replace the plywood in the floor with pultruded fibreglass more possible. I think you would agree that the interior floor is not difficult to replace. It is the furniture that I would like to avoid damaging. If I pull the floor, and try to separate the top of the plywood from any attachments, then it should be possible to cut off the bottom of the trailer and grind off any plywood that is glued to the bottom. This is much less difficult then trying to use a rope saw to cut the plywood from the outside, while cutting off the bottom of the trailer. I may even be able to make up the required extra 1/4" of depth by making the floor of the trailer 1/4" taller. However, I am also considering using 3/4" pultruded square tube, instead of 1" pultruded grating. I will have to do a cost / strength analysis first.

Now all I need is a 1979 Trillium 4500 Deluxe with a front dinette and a gravity furnace, (optional) with a rotted out floor and an owner willing to discount the trailer accordingly. Anybody?

[Island Claire]

Hi David,
the gel coat and the mat layer were attached together where it was flat, and the mat layer was attached to the plywood, again where it was flat. The problem was they had not made sure the mat was flat and properly adhered to the plywood. Production line issues, I am sure. Where it was attached I was able to pry most of the mat off with a flat prybar and a hammer.