I would think that aluminum foil insulation should be safe. Check out the following thread for some information about it.
The technique that I have documented there does require some type of adhesive to hold the foil in place along with some foam strips so there would be some question as to what would be the best choice for that. Otherwise the foil should be fine I would think.
Also you might try contacting "silver suz" in these forums. I am sure she knows about the Hawaii connection you mentioned. I believe I heard they were going to stop doing trailer rehabs but you could still find out what they used. Silver suz has serious alergy problems and I believe has decided to use foil insulation.