Hello Barbara! You might try just removing the mattress and buying storage bins that fit into the space. You could mount a long tension rod/shower rod from side to side so that when the camper is moving the bins stay in place.
Can you post pictures?
I would just remove the Mattress and Fill in the sides and use a curtain to enclose the front for easy access. Use Plastic /Storage Boxes under the bottom bed and on the top bunk. A long pole on Wardrobe fixings between top and bottom bunk to hold Clothes........
Here are a couple ideas hope they help!