Hello Again Rexlion,
Picture this: There are two separate mattresses. The mattress for the slide is ½ inch more shallow because the slide platform sits up ½ inch above the main platform. End result is the total mattress surface is level.
Now that we have established that the mattress is split. The larger piece covers the entire box, and its support is hinged so that it can be opened from the ‘living room’. And yes, there is a support stanchion so you can keep it open.
On your trip if its “Let’s stop and take a break at that next rest area” the whole top half which includes the whole bed, mattress, tent material and floor of the living area is on a piano hinge and easily tilts up for easy access and is supported by pressure struts, like on a station wagon.
Subaru. ’94 GoldWing 1500
2012 Roll-A-Home, Eagle 1 trailer
GWRRA, Thousand Trails
(We’ve downsized)