A wind turbine mounted on a vehicle will not get that much electricity while driving, but will have to be mounted extremely well, or it will shear off, especially at 65-70mph. While driving, if one needs to charge things, I'd see if another alternator can be placed which could be used for this purpose.
When parked, usually one has to set up some type of extension or tower for the windmill. Surface winds tend to be low and flaky, so one needs to get the turbine well off the ground to be of any use.
Another issue is that windmills can work in some areas (deserts, places near lakes), but would be spotty at best in others.
I'd first go with a solar charging system, either roof mounted or on a portable array. Then, see about putting a mount point on the RV for a wind turbine.