Update on fixing my motorhome leak in the hopes it will save someone some heartache in the future:
Things went... not great. I cut out the wood that was not salvageable and installed new. I used wood hardener to attempt to solidify the wood along the wall. I put lap sealant in along the wall and let it cure a couple weeks before deciding to use epoxy.
Here's where things didn't go so well. I decided to coat the now less damaged wood with epoxy, allowing it to level out. Things seemed to be going fine. After a bit, the epoxy starting reacting with something, creating heat and hardening super quick, leaving a cloudy look to the epoxy. I poured epoxy down into where I knew there was brittle wood, hoping that it would fill the crevices and help the structural integrity.
I poured a little bit and then went down below to look at the storage compartment to make sure epoxy wasn't just flowing out somewhere. It was a little warm but otherwise unremarkable. I figured that was the hardener doing it's magic. It wasn't.
Other than the small spot that reacted strangely, it seemed to be working fine so I used the whole container of epoxy (127 oz.). I went down below again and the storage compartment was full of fumes and smoke. I cleared the area and got an ventilation fan on it to try to stop the chemical reaction and cool things down. The epoxy reacted with something, likely the blue foam stuff, and melted through the plastic in the storage compartment. This is how it looks now. It is hard and I think it's structurally fine, though it looks terrible.
I then tried to do a leak check, sealing all of the vents. It seemed to be working as there was some resistance to closing the door but I didn't find any leaks. I think the driver door must be what is allowing water in as there was water in the jam. It may just be a poor design where the water sits in the door jam and slowly gets seeps into the wood.
I'm just not sure how to proceed to make sure it doesn't get water damaged in the future. The screws behind the driver door at the trim line are popped and I'm not sure new ones will take. Worried I may just damage it more by trying. I may call and see if I can get a professional leak test done and advice on how to finish fixing this but I'm sure everyone is slammed with the weather warming up. I don't think there really is a way to fix the storage compartment area, just need to clean it up and maybe put some type of covering on it.
I mostly wanted to share because I did not expect the epoxy to go off the rails like it did. I hope someone sees this that may be considering using it and is more careful than I was.
Also, be very wary of using rubber tape. I applied some along the door to try to stop water leaking and that stuff is not meant to be temporary. It's been damn near impossible to remove, even with solvents, a heat gun, etc. Wish I never saw that stuff. The aluminum tape came off fine, should have just used that. The rubber tape is now off but I don't think I'll ever get 100% of the adhesive removed.