Anything we do to try to get better fuel economy is a good thing. I applaud the idea of trying this, its a good idea IMO.
Why not put them on the nose of the pickup as well and on the sideview mirrors to deflect the sides , where the camper is wider than the truck.
I think each individual will get different results regarding mpg.
Every time i fill up any vehicle, i can choke extra fuel in to the tank . In varies on the amount . In order to achieve MPG results, the fuel fill would have to be to the same exact level each time . That might be a little difficult to do .
I would think if they helped save fuel costs, they would be on a lot of trucks. I don't see them being used on commercial trucks. Any thing i have read, they help with bugs but not MPG.
For anyone interested, i found this informative . The impact on a tc is not the same as a semi but some of the info here is helpful.
http://cumminsengines.com/uploads/docs/cummins_secrets_of_better_fuel_economy.pdf