You can insulate things with flexible closed cell foam, like say, something akin to the foam in wrestling mats. Just cut it to size, to fit around your cabinets, shelves & what not. Then get some 3M Spray Glue, & attach it right to the hull. And once that's done, you can use the same glue again, only this time, to glue automotive carpeting over top of the foam.
Then, if you want it to look fancy, odds are, the place where you snag the carpeting will have edge trim, which you can staple or glue into place. Or you could just get some nice wooden trim, pre-varnish it, & affix it to the hull + over the edges of the carpeting with a simple tube of silicone.
Such is a fairly simple process, & not overly pricey. I did all of the hull sides on a 33'er in a weekend, solo. With only a touch of supervision from a friend who'd done his boat that way.
And honestly, unless you live somewhere where it gets real cold, it's likely that just installing the carpet alone will be sufficient insulation.
That's what I did on my first boat, when I lived in SoCal. Where winter temps never drop below 40 degrees. And I had ZERO condensation, as well as being Amazed at how much installing just simple carpeting warmed up the boat. I noticed the difference right away, like right after I put it on. Even before I fired up my electric
Ah, FYI, my boats had cored decks. Which is a biggie, in terms of keeping things warm & dry, even when only using a tiny electric heater
to stay warm for the winter.
In a pinch, if you wanted to add R-value to your decks, you could get some 3mm plywood
, & pre-finish both sides with epoxy
. And then add some blue or pink board foam to the plywood
. Once you do that, & affix it to the undersides of your decks, I imagine that it'd make a Huge difference in terms of how warm things stay. Especially if done in conjunction with insulating the hull(s)... just with carpeting, or with both carpeting and insulation.
It'd be easy enough to mount some cleat stock to the underside of your deck, to which you could affix the above mentioned insulation style. And if you want things to be Purdy (pretty), platen mold
finish onto the ply prior to adding the foam & installing your new ceiling.
One can get panels
with pretty much a perfect finish by doing things that way. And again, putting in wood trim to class it up even more, with just some adhesive
out of a caulking gun's a no brainer.