They do work well, and I do think they'll preserve tire life some.... However I still state as I have for years that I'd rather go cheaper on the RV and buy an enclosure to store it in than a nicer coach and do covers and the like. (of course if it is possible in the area you live). A "garaged" coach from sun/weather will last WAY longer, look better, and won't have even close to the issues as one left outside. Dry rot, fading, paint, roof issues, funky a/c covers, etc. etc. All from weather & elements. 100k coach outside - no way. I'd go 70k coach 30k building.
4 whopping cylinders on Toyota RV's. Talk about great getting good MPG. Also I have a very light foot on the pedal. I followed some MPG advice on
Livingpress.com and I now get 22 MPG! Not bad for a home on wheels.