I don't know where you are located but the black expanding foam is typically for pond and waterfall construction. Check your local yellow pages for a pond or aquascape construction company. They might even give you a can.
Fire proof foam would be better...but then again these rigs are matchsticks anyway. If the foam is in an area that could get near 200F, I would opt for the fire proof stuff if you could find it.
The Handi-Foam listed above on the Grainger link is what most RV companies use except theirs are in large (expensive) containers and use a pneumatic gun to apply. The small can looks pretty good to me.
1998 Gulfstream 36' Sun Voyager Bus Platinum