interior panel / door insulation

[corax]

I want to caution everyone who is using expanding foam in the steel structure of their vehicles . . .

The exact reason I won't go this route, it impedes drainage and dissipation of condensation. My plan just involves putting a layer of insulation immediately behind the interior panels to reduce drafts and hopefully reflect heat back into the cab. I'd even love to put foam rubber padding under the carpet to help insulate, but I'm afraid it'll just hold moisture and start a rust problem.