I've cut foam very nicely using a knife blade in a sabre saw. It sort of depends on the foam. A dense foam cuts great with the sabre saw. The very soft stuff can be compressed and cut along a straight edge with a razor knife.

I'm sure someone has the really trick way to do it - and I'm listening for the best answer.

Are you trying to carry the B400 with the blades extended or folded? Extended would take a small suitcase so I'm guessing you are folding the blades. How long is the heli with the blades folded? And how large are the batteries you carry to charge with?

For a remote charging station I got a plastic tool box. I bought a couple of 12v batteries like the ones in the portable auto jump-start packs. I didn't care exactly what they were for so the guy at Batteries Plus was able to find a pair of cheap batteries. They were about $5 each. I wired them together (in parallel) and put a cigar lighter / 12v receptacle through the side of the tool box. And the upper tray fits into the box so I have room for extra parts and tools and stuff. I charge the 12v batteries using a 2 amp wall wart charger with a automotive 12v plug on it to match the receptacle in the tool box. It holds power for months. So I take the heli and the tool box and that's all I need.