Prodex in a floor is excellent in a cool or cold weather climate - its not so good at keeping heat from rising into the floor - specs from website:
heat flow down (1) layer of Prodex *R 15.67
heat flow up (1) layer of Prodex *R 6.00
The specifications on the prodex website are with 2 & 2/3 inches air gap. Thats easy to do on a stick built housing structure but hard to do elsewhere.
Prodex - and all reflective type insulation - work especially well at reflecting heat 'upward' and cold 'downward' - the important part to remember is it needs a dead air space to truly work.
When heated energetic air molecules slam into the aluminum its got to be reflected back without imparting much heat energy and a large air gap reduces the number of times it can ricochet around, multiply that by billions & billions of nitrogens and oxygens and you see what the score is.
I put prodex in primarily since it does not provide aide and comfort to rodents - and left the air gap intentionally small at 1/4 to 1/2 inch to keep little vermin condos out of that air gap.
The spar area was done the same way - two inch strips around the exposed plywood area edges glued on with vulkem and then the outer shield of prodex glued to those, with a double thickness standoff in the center, then tacked for a mechanical fastening with the rustless monel staples.
It's tempting to go with another layer, of prodex of something else in the subfloor area but the real deal to worry about is the roof and walls, which I have not closed in yet...
The days are short and the night is long and the stars go tumbling by.. . ~Airstream~