I live in the California Central Coast with a mild Mediterranean climate where it seldom freezes. I'm building a 5'4" wide by 10' long Benroy(ish) teardrop trailer. My goal is to keep the completed empty trailer weight under 1,200 lbs. When loaded up with bedding, clothing, food, water and other camping supplies I want to keep the weight under 1,500 lbs. I'm trying to very carefully consider the weight of all the components to best achieve those goals.
My goal is to build a teardrop that will be comfortable while camping in a wide range of weather conditions whether it's hot, freezing, dry or rainy/wet outside; that substantially reduces interior condensation, and will have better soundproofing than solid plywood does. I'm building the floor, walls, cabin/galley bulkhead, the roof and galley hatch with sandwich construction for those reasons and to better control weight. To get the best insulation value in limited space(s) I'm using rigid Polyisocyanurate (ISO) foam board that has an aged R Value of about 6.5/inch.
The floor will have 3/4" framing and insulation. The side walls will have 1" framing and insulation. The bulkhead will have 3/4" framing and insulation. The roof, galley hatch and front cabin wall will have 1-1/2" framing and insulation so they all will have an insulation value of about R-10.
I'm using 1/8" plywood inside and (Baltic Birch) on the exterior. The exterior will be completely fiberglassed to strengthen and water proof the thin exterior plywood skin. The outsides will be painted with white marine paint to protect the fiberglass from UV damage, to better reflect radiant heat, and to look good.
Which Rigid Insulation Should I Use? explains that rigid foam boards vary from about R-4/inch up to R-6.5/inch.