Collapsing Floor Fix

We have successfully quarantined the past eight months and are still alive, praise God. That being said, what has anyone tried to fix a collapsing kitchen floor on a RPod 178? Has anyone had any success using the spray expanding foam "Great Stuff" found commonly in Home Depot? I planned on drilling a number of small bore holes under a couple of removed floor tiles and hope for the best. The floor is getting worse by the day and I need a solution. A helpful Podder recommended I use a marine-grade expanding foam that actually used water leaks in collapsing fiberglass boat decks to its advantage. It sounded too good to be true and then I saw the price tag on the stuff which puts it not only out of reach but nearly in the next state. All discernable water leaks have been located, repaired, and dried. 

As always any comments or suggestions would be most welcome.

Back to my eggnog . . .