Don't overthink it, Skyman. If you are tolerably comfortable, the guitar will be be OK too. If you worry about getting too hot too fast, then wrap the case inside the dry bag with towels or a blanket for thermal insulation. I've done a lot of kayak and motorcycle camping with a guitar in a big dry bag.
BTW, I use water beads in a perforated soap dish, and don't use Humidi-Paks. Note that whatever humidity device used will last 3-4X longer in a decently sealed hard case than in a gig bag -- the zipper is quite porous.