I made a separate bunk bed for our Basestation. It looks the same as the Jayco factory bunk (brought Jayco ply wood and iron on edging and ladder mounts) but it has legs that fold down and go to the floor over the single bunk that folds down from the wall. I had a mattress made from a mattress manufacture to suit.
I have the overhead cupboard factory installed in my basestation so I made this bunk about 100mm lower than the set on the other side of the van to give a little more clearance for the person sleeping on this bunk.
This bunk all worked perfect on our last trip
Have a look at the pictures
Legs unfolded
Folded up flat to store against other bunk while transporting.
Fitted in Van (note over head cupboard )