My 5th wheel is 31' long but I made the level part of my packed gravel pad large enough to accommodate a 36' x 18' carport. Due to the contours of my land, on one end the gravel is probably 18" deep tapered back to nothing on the other end. The sides and high end are tapered down to ground level. I would rather spend the majority of my money putting a roof over the top rather than putting concrete below the trailer