Any of your suggestions would work. You would have to make sure that the glue you use to adhere the foam to the walls will not melt the foam.
Scamp trailers uses Reflectix (looks like aluminized bubble wrap) insulation with a marine headliner material glued over it. I believe the R-value is somewhere around 6 or 7, but we never had any problems with this in our two 13’ Scamps, and now in the sleeping area of our
Lil Snoozy. Most of the heat loss is from
windows and vents. Reflectix cut to friction fit over the
windows and vents at night really helps insulate.
Dave & Paula