We had amazing skies over our Bortle 2 site at Clayton, South Dakota last Saturday night.
But alas, viewing was cut short by dew by Midnight.
This Saturday I will use my Orion light shroud to battle against the dew on my 12" Skywatcher collapsible Dobsonian reflector...
I am also looking to get some foam, based on this Sky and Telescope article:
Is that called foam core? Foam-rubber? Or what exactly do I need to tell the store I am looking for?
The foam you want is a sleeping bag mat. I bought one at Walmart years ago for about $5. It comes in a roll and is made to go under your sleeping bag to insulate and protect you from ground dampness when camping.
The mat is large, and there was enough to make dew shields for all of my telescopes, including a 16" Dob. Usually people don't think of needing a dew shield on a Dob, but the secondary mirror is way up there in the upper tube assembly and might get dewed up, so it's best to be cautious.
My Dob's dew shield isn't cylindrical. Instead, it's a half-circle that's deep enough to cover a good portion of the upper tube assembly. It's secured with an adjustable webbing strap that's snug enough to keep the shield from flopping off, but loose enough not to squeeze the tube and throw my secondary alignment off. Notches were cut out of the shield to accomodate the finder scopes.
Hope this helps!