FreeBase,
You'll get better insulation if the there are pockets of air against the walls of the keggle. The best type of wrap would have an airspace with a highly reflective layer before the foam. There's a whole lot more to insulation, but I think you'll find the foam will crush the shit out of the aircell anyway.
If you just use the foam you'll get something that will take on water. The aircell version can be hosed down.
Try finding something that's heat resistant and non porous.
Niner,
What type of electric system are we talking? An internal element?
I've done 50 odd brews with insulation, but would not let an external element too close to something like this.
A fire rated foam is available if you ask around for it.
PS. Tip: Keep a sprayer with some water handy. It can help contain the blowouts you'll no doubt get, if you haven't played with expanding foam much. I've seen it lift half a tonne before without too much effort.