not sure what the cost would be, but have you considered: http://www.frolisleepsystems.com/
as a general observation, if a person can afford a RTT (or ____ whatever the $$$), doesn't it become almost worthless if it can't be used successfully?
.... I'm surprised they don't include them standard with the purchase.
Anything will get moldy if you leave it moist for too long. I've been using a couple tents for the past couple years without mats. I always open up the tent when I get home to air it out (I'd do that with or without a mat), and at the same time I just pull the mattress out and so it can dry out if needed. I've never had a mattress get moldy.without the mat, does the mattress get moldy underneath?
Driwall™ Rainscreen
http://www.keenebuilding.com/residential-driwall-rainscreen-020-1.aspx
You can tank the guys on Pirate - they tested it and it works great and does not compress.