Dave,
This is the mattress topper we have (it's actually 1.5 inch memory foam) and since we got it after the first couple of trips I sleep much better in the TM than I do at home. Without the topper I would wake up with a sore back. (I guess I should look at getting one for home too....or go camping even more often than I already do
)
We found we can just flip the front topper forward (folding it once in the middle) and it allows the back shell to clear with no problems when it comes down on the front bed.
The rear bed is fine without flipping or moving the topper.