Anything you can do to reduce turbulence will give you better mileage, quieter in cab, less buffeting in crosswinds when meeting big rigs going by on the upwind side.
The savings and effects IMHO are not worth it. Big cost, little gain. The effort to push a vehicle into the air is not as effective as reducing the vorticae behind the towed.
Aircraft are pointy on the back,not the front.
On semi trucks, over sleeper air foils are worthwhile because they are close to the van so turbulence between them there is an asset, not a detriment as air passes down the sides of the van then enters in greater velocity the vorticae behing the van reducing the 'suction' effect. Most semi truck trailers now have under frame spoilers to reduce drag. Some have spoilers on the rear doors to reduce the vortice behind the van. Dont see as many now like that as we used to.
Big trucks with a million miles to go 1-5% small savings in fuel over equipment cost, is good sense.
Is it worth it to you?
You might get a amall increase in economy, less buffeting ifrom winds Doubtful if cost over savings and comfort would be worthwhile.
OTR drivers experience on cost and effects is an opinion I want to read.