On my E-350 I added a square 3 inch by 2 inch metal tube thick enough to be stronger than the sheet metal of the frame and then I lifted the rear with a
1 1/2" stack of heavy duty washers so that both seats are 3 inches higher and sit more level than the reclining position that the RV had original, I lost the tilt down portion of the steering wheel to some extent but that does not matter, now we can drive for a couple of hours and not have back ache.
The seats are comfortable in the new position, they were to low to the floor and tilted back to far to be comfy for us, so modification and now they are perfect for us.
navegator