The tank kits are decent, but the filler neck solution hasn't been tweeked. With the tank in the highest position, it encroaches on the cross sill and doesn't allow a transition, adequate to allow fueling without setting the pump handle at the first click. With it flanged to the bottom of the frame rail, as designed, it is a few inches lower, than is desireable. In any case, there are a few trade-offs, when going the underbed tank route.
