Re: Upholstery foam..
I used foam from the Foam Factory. For the V berth I used the existing covers, that fit 4" thick foam. I put the highest density and firmest foam, "lux HQ" in (50 lbs) Then I have a 2" thick topper, with it's own cover. This is not memory foam though, it's the medium density (HD36) foam.
The combination of the firm base, with softer layer on top, is REALLY comfortable.
All foam was cut up with an electric carving knife.
What would be really decadent would be 1" of memory foam on top of the above. That would be 7" thick.