Not able to open the site.
At one point, I thought of going to a local upholstery shop and looking at the foam they had. Probably cheaper than getting a memory foam pad. There are plenty of online sources for open cell foam. Shopping this site can save some money......or not, but I'm not sure what grade of foam would work best.
http://www.foambymail.com/open-cell-foam.htmlThe other thing is keeping the foam in good condition. Having a cover, like the Cabelas pad, and the site that Richard posted(can see pictures, but not open the site), is ideal, but you pay for it. My cheap memory foam pad is not going to last a long time without a cover.
briansII