Hello - we are looking at a 5th wheel toyhauler that is an Alfa high profile. It looks to be about 12 feet high all along the length (35 feet). We are wondering if we will run into a lot of problems trying to drive such a high profile vehicle?
Shouldn't be any more problem than an 18 wheeler. There are 3 areas of concern:
One is the height itself. If you run into something which is lower than you are, that could be considered a problem. I suspect you won't have any problems on the interstates, but local roads are sometimes a different story. To minimize your chance of problems, measure your exact height, post it conspiculously in your cab, and keep an eagle eye out for height restriction signs. Also, watch out for trees over the road, which tend not to have warning signs...
The second is strong crosswinds blowing against that massive flat surface on the side of your trailer. My trailer is much shorter and although high in the front, the roof slopes down to the rear. I didn't have any problems with wind or passing trailers on a trip from Arizona to New York and back, so can't comment on how serious this could be for you, or how to deal with it.
Lastly is the wind resistance that the high front may add, depending on the surface area and the way the surface interacts with the wind. A slope on the front of the trailer would seem to be a help. My gas mileage went from 12 to 8 pulling my trailer, but how much of that was due to wind resistance and how much to weight, I cannot say. Some people claim a wind deflector will reduce the drag, but most say it merely reduces the number of bugs on the front of the trailer.