This seems like as good a time to discuss some of my materials and methods before the following pics hopefully alleviating some questions.
All of the plywood I used was cabinet grade marine ply from a local boat yard. 3/4" for the sides, 1/2" for the floor and front wall, 6mm (1/4" ish) roof and back hatch. I used Raka epoxy and fiberglass:
http://store.raka.com/6quartkit.aspx, Raka 900 - Medium Epoxy Resin / Raka 608 - Medium Cure; with Style 120 - 3.25oz (T) x 60 in -Fiberglass Cloth.
I glassed and epoxied the exterior of panels only. All the panels are either attached directly to the framework with bolts/screws or to one another with pocket screws from the interior. Once assembled all the joints were fiberglass taped and epoxied with 3 inch wide standard fiberglass tape and the same epoxy. When working with the individual panels before assembled I was limited on space so would do my 2 coats of epoxy on the glass (about 2 hrs between) and leave them overnight before moving them. Once the trailer was assembled and I was taping the seams I added an additional pump of hardener to the mix to prevent it dripping. Each mix with the standard ratio or the extra hardener ratio gives you about a 30 minute working time with this product line. 1 layer of fiberglass mat, 2-3 layers of epoxy depending on the surface (top got 4, front wall got 3 and then got painted and linex'd)
According to Raka while the epoxies are UV resistant, they last about 10 times longer covered with paint. I used an epoxy based marine self-leveling primer because it reacted well with the Raka epoxies. I don't remember the brand. For those who don't know and based on my research, marine fiberglass epoxies typically have adverse reactions with standard primers shortening the protective life of your coatings so your primer should be one rated for a similar application. 2 coats of primer overall.
2 coats of exterior oil based paint over the primer (1 gallon) of the tan. 3 coats of white
http://www.lowes.com/pd_139941-29-5530-1-30_1z0uk7k__?productId=3013309&pl=1 (you can buy it in 1 gallon cans as well and I only used 1) reflective roof coating. Really does reduce the heat absorbed by the trailer. and finally had the front wall Linex'd. I had considered aluminum plate but anytime you add a plate over wood you run the chance of moisture getting between them and rotting it from the inside out.
All the fasteners are stainless or in the case of the larger ones galvanized. All wood materials are marine grade. Coatings are marine grade. I have the windows, roof vents and windows on the doors that I can open up for interior air circulation with (2) 10 inch fans that I can run from solar, battery pack or shore power. I store it inside when it isn't being used with the vents and windows open. Too many builds that I have seen use build techniques that make me wince and materials that I wouldn't consider for interior use let alone for a camper.
The fiberglass was not a structural reinforcement for me but another layer of weather proofing. You have to remember that if you are driving down the highway in the rain, your trailer is experiencing a hurricane literally. Water will get in if you let it. I was very leery of working with fiberglass at first but after watching the videos and reading as much as I could I came to the conclusion that the Raka products were the most user friendly and I found them very easy to work with. Hope that helps.
Also direct fit replacement shocks for the M101 series trailers are either a Napa HD version:
https://www.napaonline.com/p/NS_76992
or a Monroe lighter duty version depending on your preference:
https://www.amazon.com/Monroe-32283-Monro-Matic-Shock-Absorber/dp/B0012WW44A