Source Engineering Inc | Custom RV Chassis | Eugene, OR
Call these folks. I installed one of their fans early on versus installing a Horton Fan. Easy enough do it yourself and the results were instant and amazing. Better fuel mileage, lower noise by 5 db which is less than half, and better acceleration.
You can do a search on these forums and find several threads on the issue. I would do this mod in a heartbeat. Plenty of bang for the buck. Only one drawback is a reduction in downhill engine braking due to the reduced drag of the fan.
Mileage increased .5 mpg immediately.