There's not much sugar coating on that SuperD!
We have a RV king in our ACE, one of the first "Mods" my wife did was to purchase a memory foam topper. Walmart had 2 and she selected the more expense one (of course). It feels wonderful. She had to prune it down to the RV King-size. There are mattress companies in our area that offer to make custom sizes. If it were me, I would want to tryout a product in the showroom and then see if they can make it in the size needed.