Floor Insluation

[TygerCub]

Pulled some of the matting up yesterday and found just a little bit of surface rust. I hope to finish the mat demolition today. Later this week I'll have to get in there to clean up the residual rust dust, clean the floor to get rid of any oily residue, then roll it with some Rustoleum Rusty Metal Primer. Then...

Should I lay down some 3/4" plywood over the metal, then insulation, then flooring... or should the insulation go directly against the metal, then plywood, then flooring?

I'm really intrigued by the possibility of using radiant floor heating this because I know a warm floor makes for warm feet... and warm feet makes the rest of the body easier to keep warm. I have several questions about this tech:
Who has successfully installed in-floor heating - and is using it now?
What powers the in-floor system pump? Electricity? Propane? Other?
What type of fluid runs through the piping?
Was the piping run under furniture as well, or just under the walking space?

One more question about flooring systems...
Has anyone used spray-on insulation under the bus along the outer framework?
Seems to me spraying the undercarriage versus laying down foamboard inside would offer more protection, the ability to insulate water tanks, and seal the exterior undercarriage from further rusting. Or would that all turn into a sorted mess once exposed to road conditions?

Looking forward to some interesting replies!

[NewSkewlHauler]

I've thought about the idea of radiant floor heat a lot. I'm not 100% sure I'll do it. I think that it can be done, but there would be a lot of movement it would be a nightmare to repair. That being said, I'm not closed off to the idea...I'd want a tankless unit too. But I really think that I'm probably just going to stick with using the stock heaters (probably relocated) as well as an RV furnace or a AC/heat pump roof unit (or maybe a mini split home type unit). I'm also really looking into cork flooring for a couple of reasons. 1) It's "green." Sort of...Cork is harvested from the bark of the trees every so often, so the tree is never cut down, it renews itself. 2) Cork has great noise reduction and insulation properties. I haven't really looked into the cost, and I'm sure it's going to really hurt, and I think that it'll be one of the better things I do with my bus (when I finally get it!).

I believe that LadyFranklin is doing radiant floor heat in that bus. I haven't heard from him in awhile...probably kind of like Elliot (Millicent), he's off doing "gainful employment."