[ijames]

Thanks for the links. No mention on any of the three about aerodynamics or effects on FE. I had thought about a sliding rail system but figured it would be too complex and costly. If it made a significant difference in FE I'd assume they would be bragging about it, so maybe that's evidence that the effect is in the noise. Oh, both full size units (the sliding rail so it can be anywhere from front of bed to tailgate) and the swinging box (so it pivots out of the way for full bed access) are flagged as discontinued by the manufacturers; only the fifth wheel shaped box is still for sale.