It's finally hot enough to start testing my theory.
Here's a little video of the inner walls before pouring the polyurethane.
https://youtu.be/9ipZ0UjM4BQAnd this is after the first pour.
https://youtu.be/J8z_lnoPzEYAnd this is what I observed.
After mixing the two parts for 20 seconds normally you would dump the whole thing in the hole but in my case I have to pour 1/4 of the bag at a time in 4 different places. By the time I've poured 1/2 of the bag, what I'm pouring isn't liquid anymore, I'm pouring foam.
As I was emptying the bag I noticed how hot it became, almost too hot to handle.
It was easy to see where the polyurethane went inside the walls just by touching the outside panels of the van.
Second pouring tomorrow.