We just ordered new cushions for our Liberty, for a twin bed mode. We went to the Melrose Mattress store where we originally had our 2 mattresses made for the trailer. He is taking that 6" foam and cutting it down for us to 3"... Our cushions will have 3" of medium foam, 1" of a softer foam (not memory) and then Dacron over the foam.
We found that the cost of foam has risen in the last year almost double (because of oil).. It went up for one cushion that would have been $100 - it is now $160... I was really surprised when I called Melrose Mattress... I mentioned that we weren't using our 2 mattresses and needed to order new foam cushions... he said they could cut our foam and save us $$$. He did.. We took our fabric and mattresses to him, and we will pick our finished cushions up in 2 weeks (or before).
Just a hint to get several estimates for foam before you have the job done. When I was calling around there was a real big difference. Try your local mattress shops ... some do more than just mattresses.