Stringer foam

[Moose]

Hey guys, I've got the stringers on my 74' 23sf cleaned out and I'm about ready to fill them back up and continue on with the rebuild. I was wondering what type of closed cell foam to use, like specific brands and densities? How much foam am I going to need? Also, is there anything I should know before doing this? I was thinking of maybe bracing the stringers shell so the foam doesn't make the fiberglass expand or anything like that. All input is welcome. And if anybody could explain how I upload images to this post that would be great also.