our hybrid has a short queen heated mattress, and I put a 3' standard queen over top of it. I like how it fills the space of the bed platform. The stock mattress has space all around it, so when we put the memory foam topper in, it filled it quite well. Now we have a standard queen sleeping area instead of the short queen. My feet will never know the difference
Oh...and the heated mattress works just fine under the memory topper. Warms everything up real nice. In the summer, we'll switch it around so the foam doesn't warm us up. We sleep on a tempurpedic at home, so sleeping on the Rockwood stock hybrid mattresses was not an option for us. IMHO, my 1992 coleman pup foam mattress was much more comfortable.
2014 Rockwood Roo 23IKSS
2012 Dodge Ram 1500 Hemi 4X4
Me, Hubby and Luna the Lab