Trailer came with queen mattress, but not enough support

If you make a larger support for your mattress, will you still be able to walk around the sides of the bed?

And, if so, why not just build a new, right-sized flip-up part with side supports and replace the original section? You could likely use the same hinges.

Front-facing doors on the underbed storage area would be great. Drawers would be even better, imho.

Good luck.