Anybody fill the area between the trunk / fenders?

We are replacing the patch panels on my Demon and the trunk extensions are pretty much still there but are missing some in the front. This has been a race car a long time and I think the burnouts took their toll. The body guy is thinking of filling the area between the new patch panels and the trunk extensions. Supposedly this "structural foam" is the solution to moisture getting in there, as well as crud and debris.

Anybody ever do this? What do you body guys think?