I added the 1" pink foam board between the bed and the mat before loading on my Lance 845 and it turned out that it was not needed. I left it in as it adds some insulation at the bottom of the camper where otherwise there is none.
The newer campers built after the change in the siderail height by the truck manufacturers allow for this change.
The extra height above the sides of the truck does make it easier to reach into the area where I feed the coax cable at RV parks. My 2008 model does not have the external coax connector (or a number of items that are shown on the 2008 Lance brochure for this camper).