RE: :Tip for Rx. padding
I'm with Bill on the expanding foam issues. It dries fairy rigid and will transmit a lot of vibration to anything "wrapped" in it. As filler or for flotation .. no problem.
Personally, I use Foam Rubber carpet padding as my "replacement" for hobby brands of foam rubber, although I still tend to use it as "filler" with a single layer of Hobby foam rubber directly around my receivers. Too much at stake to gamble here!