I would assume that for "your needs" you mean watching a trailer? Because I installed a tag mounted license plate camera on my buddies 05 F250 and as a backup camera it's perfect, a very wide angle and it's just the right height. When you put a trailer on there, it's a bit low but not too bad. His trailers have low edges (motorcycle and quad trailer and towing) and it works pretty well, mainly cause the F250 is very high up as it is. If it was in a corvette or something it might be a bit low. His hitches have a good drop on them because even stock, the F250 sits very high up. I never took a picture of the rear view camera with his trailers attached....
Of course when you hook up a trailer, put your head at whatever level and see how low you can go. Only you know what you are doing. I can't see too much benefit of getting the camera up 2 more feet. Maybe 3, you can't get too much higher than that.
I'm not sure what your needs are and why that might not work, but they are much easier to install and I thought it worked very well in a F250. It was one of these:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0093072441
The one bobmun posted other people have installed with decent luck, but I can't just bring myself to drill any holes in a vehicle of mine like that.