I had a similar failure on my '81 Scamp
. Unfortunately, this happens top lots of fiberglass trailers. The problem with having the resin/glass under the plywood is that it keeps water from getting out
of the wood just as well as it keeps it from getting in. Even small leaks
, side rivets, etc. can dribble enough water in to do this.
I'm replacing my entire floor with marine plywood. I used material from a local specialty distributor which also contained some flame retardant, probably borate, which interfered with curing of the repair resin I coated the bottom side with.
Most marine plywood won't do this. However, I strongly advise testing the resin on your plywood before attempting the actual repair just to make sure there is no reaction (or lack thereof). If you shop on-line for marine plywood for pontoon boats, you'll likely find the right stuff. You may, however, end up paying more for freight than plywood. I also noticed that common permanent marker ink turned the resin into slimy goo! Make your cutout markings with a carpenters pencil.
The resin itself is common peroxide-cured polyester / styrene - the same as you would use to repair a car or a boat. 3M/Bondo makes it (don't use regular Bondo body filler!) as do lots of other companies. If you want a stronger resin, use vinylester, which will stick to the existing resin just fine, but costs quite a bit more. You can get all kinds of fancy resins and fillers from specialty distributors. Just google fiberglass resin composite distributor
with your zip code and you'll find tons of them. Auto body repair or boat repair supply houses have lots of the same stuff. The resin needs to have fiberglass added to it, whether it's chopped strands or glass cloth. The easiest thing to do is buy the resin with chopped glass added to it already, since it doesn't look like you'll need to patch any structural joints. Woven glass cloth saturated with resin (without the chopped glass) is really good for that. You can find the premixed resin and glass at lots of auto parts shops and big-box stores. I bought my Bondo-Glass at a local farm supply store. Bondo(R) Bondo-Glass(R) Fiberglass Reinforced Filler, 272, Quart (US) Can (Net Wt 2 lb 9 oz), 12 per case
Unlike my rig, yours has a resin/glass bottom with wood over it. Cleaning out the inside of that panel without going through it may be a challenge, depending on condition and thickness. It may be prudent to sand and recoat the underside with resin after the wood replacement. just to make sure any holes are sealed.
Just like painting
, body repair will fail without proper prep. You absolutely have to get the old surface clean before you start. Having air-powered tools is a big help, but not absolutely necessary. I used a cheap air die grinder with a double-cut carbide burr to cut old glass/resin out, but you could use a Roto-Zip for this as well. A high-speed sander or angle grinder will clean away dirt from the surfaces you need to bond to. Flap sanding discs and wire brushes may do less collateral damage than simple sanding discs. Clean at least a 1" wide band going up the wall to ensure a strong bond. Vacuum thoroughly and then clean the surface with acetone on a rag. Wear nitrile rubber gloves and do this with LOTS of ventilation.
If using power tools, get a good HEPA or ULPA dust filtration mask. Wear eye and ear protection when sanding or cutting. Wear old clothes you can throw out when you're done. The dust may make your shirt permanently itchy.
There are lots of good how-to tutorials and videos on youtube and resin manufacturer and distributor web sites. Most will be specific to cars or boats, but the materials and methods are basically the same, especially when it comes to wood/glass repairs on boats.
The remains of that bolt you dug out aren't very recognizable. I bought some closed-bottom threaded inserts and an application tool from http://www.mcmaster.com
to reinstall my floor. You may need to do the same. Somebody who is familiar with Trilliums may be able to steer you to the correct fasteners to use. That water may have corroded your frame where the fasteners went in. Make sure that connection is really solid. You may need to drill new holes nearby and and seal the old ones.
Oh yeah, don't forget to find out how that water got in. You probably won't want to do this again in two years.