J wrote:
We have an old hot tub on our deck. One of several issues with it is
that mice have been tunneling in the foam insulation that resides
between that tub and the wooden frame.

I've shop-vacced out as much of the debris as I could and now I would
like to fill in all these tunnels and voids (some up to several
inches in diameter), but whenever I read the instructions on cans of
spray-foam insulation (like Great Stuff and Touch n' Foam) they state
that they are for filling cracks and small gaps and will not cure
properly in enclosed spaces (even the Great Stuff "big gap filler").
On the other hand, the kind of spray foam used to fill walls and
rafters seems like overkill and much too difficult for a small DIY
project.

Is there an appropriate product to use for this job? Is the best
solution just to use the Great Stuff and hope for the best?. I could
probably fill the larger, easily accessible voids in layers, but for
the tunnels, it would be nice to just spray something in there and
have it fill the thing up. The gap between the frame ranges between
about 3 and 6 inches. I think the tunnels really snake around in
there.


Check out 2 part expanding foam.
https://www.google.com/search?q=t2+p...expanding+foam