I've used this product for insulation: Reflective Insulation | TempShield Double Bubble White Foil Insulation
Using a 3M spray adhesive once that's cured there's no out-gassing at all.
I used the foil side against the bare sheet metal of the interior walls and ceiling, double layer including dropping the front headliner. Along with unfaced fiberglass bats inside a few selected open body cavities this gives pretty amazing sound attenuation along with a relatively small degree of actual heat/cool insulation.
Adding a 3/4" plywood floor is a huge sound killer---the amount of noise coming through the floor is eye-opening. With careful fitting there's no need for screws etc to hold the plywood to the body. Drilling holes into the body is a sure way for rust to begin, assuming you live in a four season climate.
Side wall insulation is best with rigid foam high efficiency panels. This does require a bit of cutting and fitting if any sort of paneling will be installed---the end results worth the effort though.
Hope to hear and see more of your project as it progresses--should be a lot of help available here.