Here is a lesson I learned, this being my first build. Insulate the floor!
Our old rig had no floor insulation, It was cold, even frosty in the mornings in winter. I had planned to add some under the floor, to fill the cavities between the tubing that makes up the floor. So I did not put anything other than a 1mm r.5 piece under the vinyl flooring…. Partly because I did not want different floor heights, but I had plenty of head room. I should have added 1/2″ at least under the flooring. that is my lesson. Once I did get around to insulating underneath it did not do a whole lot. The floor is steel and it just sucks the cold right through.
But back to the floor insulation. I just the same type of closed cell spray foam, this time a DIY kit. It was messy, very very messy. I taped off the frame rails and down, covered the axle, drive shafts etc, then got into a big tyvek suit and put Vaseline over any exposed skin…. And got to spraying on my back. Not a fun task.
The underside did get well covered. It looks like a badly frosted cake, but should be pretty well insulated, its about 2″ thick most everywhere. I think the biggest benefit we will see from this is that the heat from the drivetrain will not come up through in the summer keeping it cooler. It got warm pretty quick once we parked.