Your looking good so far.
The problem with spray foam is that is won't allow water to get out. It seals any water against the wood. Many of us have used some sort of rigid foam product and made sure water has a path to exit if it gets trapped in there. Drains of some sort in the belly skins is not a bad idea. I got rid of the bumper plate at the back and the storage box that tends to funnel water under the skins.
Here is something about the bumper plate ectomy.
Here are some photos of my rear end center bath rebuild and some of the front as well. I am sorry for the disorganized mess. I have not have time to edit everything down.