If it's any thing like what I've work on before you'll find it's a big wooden box set on a metal frame. You should find the wooden frame work under the underbelly fabric. Floor and frame are built first stuffed with insulation covered with membrane, flipped and set on metal frame. My membrane and insolation was pinched between metal frame and wooden floor frame. As for insulation mine was regular paper backed like you find at Lowes or Home Depot. But you won't be able to get it in exactly like it was because of the way it was originally built. It took 5 weeks for my floor and wooden frame work to dry out. I used a moisture meter, Moisture Test Meter at Menards
to keep tabs on dryness of wood. Of course that was in middle of a humid summer. You don't want to cover wet or damp wood because mold and mildew will form. It's not hard but time consuming work and allot of time on your back. At times you just have to be inventive.