The door on my '85 Burrito is not the same shape as the opening and does not fit as it should. It does not curve in enough at the bottom to fit the opening properly. I have made do with differing thicknesses of door edge seal rubber but it still is not to my satisfaction.
My door is made from an inner and an outer fiberglass form, each of which have a generous gel coat on the outer surface. In the hinge area there was wood blocking at one time, but that is mostly rotted away. I did not see signs of wood anywhere else nor did I see any metal strips. However I never took my door apart. What I did do was to seal the 2 sides together properly with thickened epoxy and force epoxy into the hinge screw holes (several sets of holes) with a syringe. This made the door water tight on the inside and provided secure attachment points for the hinges.
Your hinges also differ from mine. Mine are the more commonly seen refrigerator
hinges that were used on the 80s Burros.
My advise is to keep fitting your door to the Burro as you rebuild it to make sure that the final shape will match. Also, if you plan to replace the wood floor or repair it near the door, do that FIRST, as this will change where the door hits or change the lower shape of the Burro itself. You also will need to reinforce the hinge area on the Burro, as the wood backing in these commonly rots away also. The lower one is easy since it is exposed, but the upper is glassed with Gel coat on inner and outer and will require re-glassing the repair.
There are several threads here regarding Burro door repairs but all indicate that there is no easy fix. You actually have the best chance of getting a perfect fit since you are rebuilding the door and can modify the shape.