I'm looking to organize my magazines in ammo cans and I'd like to use foam inserts for better organization in the can and to protect the mags and whatnot, but those foam inserts are not cheap. We're talking $15 for just the inserts on top of the cans that cost $10-15. What are my options for foam blocks that I'll cut to size myself? What about using spray foam and filling the ammo can with it and then cutting the pocket for the mags to sit in? Really just looking for the cheapest option that will work with my $3 Harbor Freight cans.