ctcamper is right about watching over hangs and branches in remote campgrounds and national parks. I have only damaged my previous RV's by hitting obstructions that were up high and difficult to judge.
To help solve that problem with the MH I used a camera. I already have a 7" LCD monitor mounted on the dash that I use to display a engine monitoring system (VMSpc). The monitor had a few different inputs available, so I ordered a small stainless cased infared camera from Tim at RVcams.com. I mounted the camera on the front of the RV looking forward. Now when I pull into an area where clearance is an issue, I push a button on the monitor and switch the view to the front looking camera. I get a panoramic view in front of the RV, 12' off the ground. I measured the height of my MH, both at the roofs edge, and at the highest point on the roof (the vent cover) and transfered the height measurments to the LCD monitor. Now if an obstruction is in question, I can see if it is going to become an issue as I approach. If it looks like there is going to be contact I stop and get out and look.
So far it has worked well, in 15K miles the roof of the MH is safe and sound!