Radio, we just upgraded ours as well, as the cheapo factory mattress in our Gulfstream was just sumpin else to try and sleep on. So after looking around in stores and on the net, I gave this a shot
http://www.amazon.com/gp/product/B000LQB2PU , went for the 'free shipping' option, which got it here just after the 'windy weekend adventure' in FDR state park last weekend.
After the thing 'reinflated' itself out of the super tight shrink wrap, it's about 3" thick like the ad said. And WAY cushy. We're trying it out this weekend.