Hi bills4x4,
Welcome to the Heartland Owners Forum. There's lots of useful information here along with a great bunch of friendly and helpful people.
The mattress is supported by a wood platform that's pretty sturdy. If you're asking about the mattress itself, and how much support it provides, most people would probably say you should be prepared to find something more substantial.
We have a 12" memory foam mattress from
lastingimpressionsfoam.com.