Home Guy wrote:

Any other ideas?

I see that there's 2-part expanding foam that comes in variety of
densities, for marine use, hobby, etc.

So you mix 2 parts, and you have maybe 30 seconds or a minute to pour it
before it starts to expand.

The stuff you buy in an aerosol can - is that 2 parts (and if so, how do
they keep the 2 parts separate)?