The older trailers had a sort of vinyl inside covering. Yes there is some wood in there. But be careful if you drill holes to mount anything you don't go through.
I mark the drill bit with a bit of masking tape at the depth I want to stop at.
You can of course rivet hooks or hangers to the door, it's what the curtain rod hooks are held on with on my scamp
I would avoid having much additional weight
on the door going down the road. My concern is the extra weight
would be magnified going over bumps and either pull out fasteners or put too much strain on the hinges.
Those pouches for small items sound like they would be easy to just un-hook and roll up to stow while traveling.
Someplace on the forum I saw pictures of small narrow baskets that someone hung from the fiberglass surface with those suction cup hooks for window sun catchers. Don't think the suction cups would work but the small baskets might work with hooks fastened to the door. Again easy to remove and stow for travel so the door and hooks don't take the pounding of going down the road.