Teardrops n Tiny Travel Trailers

I'm early in my teardrop planning process and need some advice. I've read a ton on this site and have a lot more homework to do. For now though, I'd like some feedback on what I have planned.
I'm currently having a 5x10 trailer built for our tear. I'm wanting to build a Grumman 2 but resized up to 6' x 11'5'' roughly. I went with a 5x10 because I didn't want the trailer fenders/wheels super wide. I think the trailer extending over part of the fender and extending beyond the 5' width will be fine. I may or may not add bracing from the trailer to the outer edge of the trailer.
We are a family of three so we wanted the bigger size to accomodate a bunk at the galley end of the sleeping area (cross wise).
Our camper will have to sit outside all year, so I need it to be super watertight and able to withstand the elements for a long time. Aluminum is great but there is always the possibility of seam leakage, wood looks beautiful but there are seams there as well sometimes. So what I'm thinking is either wood or foam or hybrid construction covered with fiberglass and epoxy and then painted with automotive paint. Fiberglass tape seal the edges. Seems the most resistant to outside exposure. I've done some fiberglass work before.
I'm a bit intrigued at the foamie idea. Maybe 2"foam walls with 1/4" interior plywood skin, exterior foam fiberglassed (no wood skin)? There is a commercial walk in cooler factory here local that uses thick sheets of the blue foam. Either 2" or maybe even 3" Maybe they'd sell me some.
Then for the roof, two layers of 1" foam kerfed, and 1x2 cross braces and fiberglassed.
I like the flashing idea I recently read about using along the bottom of a foam build to resist road debris damage and so forth.
I plan on making the floor out of plywood only. 1/2'' probably. I don't want the trailer to weigh any more than it really needs to but I'm pulling it with a truck so it doesn't have to be super light either.
I want to use a commercial made door from the teardrop supply place. Here's my question on that - with using foam (or plywood) does the door ever not feel solid when opening or closing it?
Does all this sound ok or am I crazy?

Where are you located at ? maybe you could get a tour of a foamie ...

That would be great! I'm located in mid-Missouri.

I'd use 1/8 ply or door skins if you want to cover the interior with wood. It would save a bunch of weight.
2" foam should be stiff enough with a 1/8 cover for almost all situations.

Awesome, thanks Pete

On TPCE I am currently working on two layers of 3/4 inch foam for my roof and hatch. If I had it to do over I would have used a single layer of 1-1/2 inch thk. The two layers are just taking extra time and adhesive with no real added benefit.

Edited to add: Also, at 6 wide I would consider using all 2x2 spars. At 64 inches wide I have had some bowing with my 1x2 spars. Not sure if it is changes in weather conditions (swelling) or the spring from my arched 5 mm ceiling panel, so your situation may be different with 2 inch thk and no wood inner skin. If the extra weight of 2x2's is a concern (doesn't sound like it is) then use select clear cedar like I did.

The best decision I made in my whole build was to use good grades of cedar for most of the structure, and 5 mm marine spec. ply for the skins and cabinet panels. The cedar is light weight, rot resistant, and, although it cost a bunch, the defect free straight grain of select grade has allowed me to use almost every little bit of it with out having to dodge knots or worry about weird grain. For the hatch hinge spars I stepped up to oak for its ability to hold screws.

Great tips KC!
I was wondering about the 1x2's. It's hard to get them good and straight. I recently used some cedar 1x1's for a different project and they were great to work with (and straight). Good tip on the cedar. Shouldn't cost too much extra to use cedar.

All of mine started out as four 2x10 at 10 ft. Haven't seen one knot that was any bigger than spaghetti: $600. I haven't regretted it once, not once.

"The quality is remembered long after the price is forgotten, so build your teardrop with the best materials..."

The 2x10 are generally southern yellow pine. This species is stronger and more dense. I good suggestion is to cut 2 or 3 extra spars and let then set a few days to grain release. If they stay nice and straight you will still find a use for the extras somewhere in the build.