I just wanted to post this in case anyone was considering doing something similar.
My sister had this Ford ranger that was continuously burning through alternators. Lots of parts replaced, no change. Couldn't figure it out.
So I installed a "solar alternator". Two 230 watt poly panels over the bed, an outback FM80 charge controller, and some extra AGM batteries to keep the voltage up during the night.
MPG seemed to improve by around 10%. The majority was probably from the lack of alt drag, but I'm sure the smooth bed cover improved the aerodynamics some too.
If I was doing it again I might consider a 24v system in the bed with a DC-DC converter to keep the main battery at 14.5v or so for a hotter spark and brighter lights. But it worked great as it was.