What kind of glue are you using Peter? I am trying a form of the sandwich idea on one I'm building now (kinda by accident), though not with foam. Been following your trials and tribulations with great interest.
Talking about cold weather right now sounds very cruel to those of us enjoying 105 (40 C?) degree weather here in Texas. My shop seems a bit hostile by mid afternoon.
I'm glad I have been of a little help.
I started by using Elmer's yellow glue when I first started making instruments, that was made in the USA but they stopped importing it (is it still made in the US?), so I then changed over to Syntac AV180 that has now been taken over by Bostic and they still call it AV180. I use this yellow glue in all applications as it has a very fast tack time, so fast that in warmer weather I can take out a veneered end plate from under the book press within 20 minutes or so. The only place this glue has let me down is when I'm gluing Huon Pine because of the high resin content, I then use Selleys PVA, but this is very slow drying in comparison.
It was down to 4 Deg C in my dirty workshop on Friday, Just as well I had got the spraying done earlier in the week, otherwise it would never had dried.