PVC Foam floor, not plywood?

I am facing the floor and stringer replacement project this fall 1984 SN with 2300 hrs on the meter, it has earned a new floor.( needs some engine work, but it will have to wait)....we are carefully walking around on a very rotten floor.
Has any one experience with the closed cell green foam they use in yacht building? I used it in the floor of a cabin cruiser I had and it went down great, I just did not keep the boat long enough to pass judgement on it.

Also looking for some advice on alignment, if I leave the boat on the trailer, will the hull change shape ?
I know newer boats no longer use wood in their stringers, would I dare attempt same? or would the hull flex change too radically?