Floyd's bed idea is probably the simplest mod to make. Just make something that's the same height as the bed platform, the width of the aisle, and long enough for your legs and feet. Then make a cushion that more or less matches the height of the existing seat cushions you'll be sleeping on. Adults sleep in the middle with their heads under the rear window, and one kid on each side. You could nail that platform together for less than $50, I bet.
If you wanted to have a more comfy bed mattress, consider what Thom and Cari (member name 'Accrete') use: the Froli system is a bunch of little springs that snap together to produce any size mattress you need in any shape configuration, even an irregular shape like Floyd's. Top the Froli with a foam mattress topper, and sleep well. This would feel much better than the seat cushions (leave them in storage until ready to see the trailer).
In case you haven't figured it out, a porta potti is like a box with upper and lower pieces that snap together. The lower half is the holding tank, with a fold-out spout for emptying and an open-close knife valve for 'flushing'. The upper half houses some fresh 'flush' water, the lid, seat, and toilet bowl. To empty, you unsnap the top half and carry the bottom half to wherever you'll empty it. It's similar to a cassette toilet, but whereas the cassette toilet is built into the trailer with an outer door for cassette removal, the porta potti is a separate, loose toilet that just sits on the floor wherever you want it... very easy to move around.
To every thing there is a season, and a time to every purpose under the heaven... --Ecclesiastes 3