Yeah, I am aware and not terribly happy about the weight of the thing, it will be on the ground, probably with a lumbar frame under it so that it's not actually touching the ground. I'm also thinking of assembling it with bolts and threaded inserts rather than wood screws so that it will be more collapsible if I ever need to move it or otherwise disassemble it.
The density is why I was suspicious of using flex watt, I guess I'll just have to pick up another RHP. Do you think running a moderately sized one all the way to one side would create enough ambient heat to carry all the way to the other side and get it up to the proper cool side temperature?