I have the electric hydraulic slide. The last few inches were where we had to jack it up a half inch to clear the stopper. No rollers on this just a skid pad at end of carpet. I did not touch carpet.
The beam that we used is standard 2x4 14 ft.6 long and then a 1x2 attached to duplicate what was there for the metal frame and seals.
I replaced the inside seal that the removable wood frame hides and the outside seals. This old Wilderness is in great shape other than what we repaired and it was well worth the effort as we are off season in my construction work plus I had access to shop.