Read the post before yours- under the bed is NOT an option.
On the permanent bed: the Campster
bed is originally about 72 by 76 or something like that, longer front to back. To get in you have to climb in from the "hallway" or galley. As I'm not 6 feet tall, I can sleep sideways, so what I did was put a 3/4 mattress (6 foot by 48 inches wide) across the width of the trailer. That leaves the two 24x24 inch seats (I got cushions for them from another member's Casita
side dinette.) I already had the mattress which was custom made for a 3/4 bed (antique 4-poster) that I own, but was a bit too small for that. It's basically just a good quality foam mattress.
To add a more level surface and good support (no sag in the middle) I left the table top in place as a support but added plywood crosswise over the seats. I made cuts in the seat lids so the last 24 inches still opens for storage but there is currently no way, without removing the mattress and boards, to access the front 4 feet of storage.
I really don't use those seats as seats. As they are a bit lower than the bed, though, my dog does use them as a jump up to the bed, so the one on the trailer's right I keep pretty uncovered. The other side has traditionally been where my "stuff" sits in camp. Duffle bag, iPad, etc. This didn't leave a very good place to put things like a cup of coffee or soda or eyeglasses at night, so one of my goals with the storage drawers is to double as a bed table.
I could travel with them under the bed, but I already have other things under the bed. I definitely don't want my clothes stuffed under the bed when I'm in camp.