getpower1,
We noticed adding a memory foam topper on the OEM mattress in our TC's would also interfere with the wardrobe door being able to be opened. Too high or thick! Just another reason not to have the OEM mattress and having to add a foam topper so it's more comfortable and gives more R-value. Knowing this as we'd checked the dimemsional clearance be for buying our first air mattress, we bwent with an 8" thick one and it doesn't even need a foam topper because it's button push inflation infinitely adjustable inflation. Mattress thickness is usually not an issue with a TT, MH, or 5th wheel but sure is on most TC's cabover beds.
Also learned that any added insulation under a TC bed should be under the mattress as you want to prevent any thermal difference sweating before it can get the mattress wet as mold will grow under it. We use Astro-Foil and some have used closed cell foam board but thickness needed for R-value can still be a problem. Never had any sweating using the Astro-Foil since 1988 and many nights sleeping in -10 F or lower outside the TC temps. Always 70-72 F inside our TC or RV 24/7. Neither of us like to sleep in cold air and especially not when having a bunch of heavy or thick blankets on top. Just a thin blanket or a top sheet. We don't and won't sleep in a cold torture chamber in an RV or at home.