I am sure there are better ideas and info out there, but....On our boat we used the plywood/corecell foam sandwich construction for the deck. We don't get condensation on the inside of this. On the walls and on the bow/stern areas where there is no sandwich construction we get condensation. I forget how to spell corecell. We got ours from Noah marine in Canada. If you don't need structural strength other foams would be less expensive. I would check to see what kind of foam the Clements used because I think they found less expensive foam.
We have a friend who fell in love with Arctic sailing in the north of Norway. When he looked at our Tiki 46, he commented that if we ever wanted to sail in cold climates, we could easily make one hull into a heated living area for eating and sleeping and insulate the inside of the hull skins with cheap styrofoam 20 mm sheets cut to fit temporarily inside between the stringers. I must admit that our friend had glorious photographs of the Arctic, but it is not the kind of sailing everyone would want. Nev will not go where it gets that cold for very long although we often have a few days of freezing temps at night during our annual migrations and wait for warm enough temps to melt ice on deck before sailing off in the morning. Condensation is a problem inside the boat in extremely cold conditions without insullation on the sides of the boat. Our decks are insulated as per plans and do not have condensation problems.
I sailed my old uninsulated monohull in snow and ice and blizzards years ago from New York to Cape Hatterass and the major problems were condensation running inside the boat with resultant mold growth, slippery decks which were a danger, and frozen lines making sail adjustments difficult. I put old plastic box lids in the backs of lockers to keep clothing etc free of the running condensation and I used a lot of salt on my deck to keep the ice problem under control and shoveled snow without damaging the decks by using a plastic dust pan. Lacking any heat, I just kept adding thermals under normal sailing clothes and kept fairly warm with three pair at once sailing through a blizzard which was not predicted.
The real solution to all these problems in my opinion came when I gave up coastal sailing in those conditions and simply sailed offshore from Beaufort, NC crossing the Gulf Stream in hours, and arrived in Bahamas three days later wearing shorts and tee shirt 90 % of that leg of the trip.
My Arctic sailing friend had the type of heater that did not add to the condensation and other folks will know better about that topic. He wintered in the extreme north of Norway quite happily one year but admitted to wearing his Union Suit all winter long.