I restore vintage trailer trailers as a hobby and I prefer to use the bubble foil insulation, [http://image.made-in-china.com/2f0j0...il-DBF001-.jpg
] or the stuff used to wrap hot water heaters in homes.
It is cheap and easy to work with, it is the same basic stuff that can be bought at almost any big box store in rolls.
You can see the hot water heater blanket used when I restored our 1965 Scad-A-bout teardrop trailer 1965 Scad-A-Bout Teardrop Trailer: Insulation Completed
The hot water blanket stuff is fiberglass between two sheets of reflective foil. I prefer the bubble wrap more, but did not discover it until after the teardrop was completed.