Fifth wheel rail kits like the Reese kit part # RP50054-58 do not fit with B&W Turnoverball gooseneck hitches installed at the same time. They would interfere with each other. Your best option would be to use the B and W Companion Slider hitch # BWRVK3400 which is a slider hitch that fits directly to the Turnoverball gooseneck hitch you have without needing any type of rail.
If you already have a slider hitch though and do need a set of rails like what the Reese kit offers you could instead... view full answer...
Yes, the Classic Accessories RV Cover part # CA80104 has adjustments built into it so that the extra material could be cinched down and the fit would be tight. view full answer...