Updated: Jul 6, 2020
We're just about finished with the house and barn and can finally turn our attentions back to the bus.
Started installing the insulation and new subflooring. I went with 1.5 inch Foamular 150 glued down with 3/4 t&g plywood. We decided not to do any framing for the floor and glue the foam directly to the steel. Foamular 150 is rated at 15 pounds per square inch and the 3/4" plywood on top will distribute any loads so framing was not needed.
We used a generous amount of glue that was approved for use with the foam.