Desert Captain wrote:
Another factor that contributed to its efficiency was having it mounted so far back, at the rear of the shell. I doubt it would work as well if i thad been mounted on the cab of truck with no shell.
This is why semis use them effectively on pretty much all standard trucks. The trailer and hitch are largely standardized, so the deflectors can be tailored to match very closely to the front profile of the trailer with a very small gap.
It also helps when semis drive 50-100k miles per year, so small improvements to MPG quickly add up to a lot of $$$$.
For RVs, the truck profiles, trailers and hitch setups are all over the place and too few miles to get a really good idea of the impact, so while great in theory, very hit and miss in practice.
I've often thought that a heavy canvas that extends from the back of the truck cab (you could use the stake holes in the pickup bed) to the top leading edge of the trailer (sturdy attachment points would be needed) should be quite effective. The trick is developing a system that deploys quickly and easily and can accomodate turns.
But reality is most RVs only travel 2-3k miles per year so for most even if it does make an improvement, it's still not cost effective.
For the OP building his own, the cost should be pretty low and there might be an improvement but the data provided isn't clear.
