I'm planning to insulate our V-berth with aluminum-covered flexible bubble-pack insulation. Home depot sells rolls of the stuff relatively cheaply. We'll cover it with a nice material and glue snaps to the headliner. I'm planning to install it under the shelf and wrap it slightly under the cushion. It isn't really a matter of insulation (we have warm blankets for cold nights) but if your blanket gets pulled up along the edge and you roll over, the sensation of you naked butt hitting that cold fiberglass is one that stays with you for a while. ;-)
Wally Kowal

We live aboard year round on a 30-1 in Port Credit, just outside of Toronto. There is more to insulation than meets the eye (butt). We found that lining as much of the inside of the hull as we could reach, including the deck of the V-berth with 1/2" closed cell foam seemed to get us off to a good start. (The aluminum backed bubble wrap would be a good alternative but if you sat on it, the bubbles would pop.) There are, however, some areas that need a little more and the V-berth is one of those areas. The 30-1 has a 25 gallon water tank under the V-berth and it gets as cold as the water outside the boat. We have seen another boat that had the following cure and although we have not done this yet, here is the plan. Line the deck and sides of the V-berth with 1" Styrofoam SM covered with 1/4" teak marine plywood. We would start by epoxing 3/4 by 1" ribs to the V-berth deck and insides of the hull to hold the Styrofoam in place. The Styrofoam would be cut into strips to conform to the curve of the hull. It would be covered with the teak plywood and varnished to match the rest of the interior. There would be hatches cut into the V-berth deck to allow access to storage and the water tank. We would carry this treatment right up to the underside of the deck and to the forward side of the bulkhead to the chain locker.

The boat we saw this done on was a Grampian 28 and it literally eliminated condensation in cold weather and kept the boat cooler in hot weather too. Varnish on the interior teak instead of oil seems to go a long way in making the boat feel drier too. If you are near to Toronto, come take a look.
Steve Scott --"Oyster Bay"

In the end we covered the whole area under the cushions, rolling up the sides somewhat, and cut it up a bit to allow axcess to compartments below. Did not attach. We vented all compartments with SS louvers (cutting a hole in a boat anywhere makes any owner get the shakes big time). Next fix was, solar vents. Cannot say enough. We now have had no mold, I mean no mold.
Hope this helps,
Don "RAINBOW"