Rather than deciding on a final floor for the van, I decided on some cheap 1⁄4” Maple plywood from Lowes and remaindered paint. That will let me build a template floor and test it out before deciding on a final floor.
My plan for the floor is to build something completely removable. Many people will glue down their floor to ensure it’s secure, but I’ve decided to anchor the floor only at the 8 lashing points. Simple and easy to change out later if needed.