I have put a 1 3/4" memory foam pad on top of the OEM mattress in my 3326King. I love the mattress and would far rather sleep there than in the house. I got it for $60 on
www.overstock.com. I do have a problem closing down with it. The rear latches are about 1/2" from closing and it takes a struggle to get the top down and latch closed at the same time. I find the 2 lamps in the rear bedroom put indents in the memory foam, so they are the primary culprits.
According to my measurements, one could say that 1 1/4" memory foam would work and the top would close properly and easily.
I have been wondering if replacing the OEM mattress with memory foam wouldn't be a better idea. Has anyone tried this? Can the mattress cover be disassembled? I am pretty sure the OEM thickness would be sufficient to get full benefit from the memory foam. The Overstock.com mattresses are about 6" more narrow than the TM king bed.
Bob