I rarely take a small back road. But I do have to now and then hauling heavy equipment. Tree limbs are more likely to snag you than anything else since their height changes as they grow and become more heavy. In almost all cases where there's a low bridge or man made obstacle on a road way there should be a warning sign. Almost all bridges on major highways and interstates will be much higher than your trailer.
Now and then some cable television or phone installer may be remiss in his job and hang a service cable too low. I snagged one on a state highway and I was under legal height a while back. I took down about a hundred feet of single service cable along with the connectors from both the house it was attached to and the poll it started from. But I was under legal height and it was their problem. If it had damaged something I was carrying I would have filed a claim with them to have them pay for damages. But I was carrying a big excavator so I had no damage. When they installed a new cable television line to serve the road I live on they hung it lower than the legal height across my drive and had to return to raise it higher. I had to prop it up with some 2 x 4s until they fixed it. So it is possible you will find something too low to get under. But your travel trailer is under "legal" height. That doesn't mean you shouldn't use caution and watch out for low stuff.
I tow a 40 Jayco Talon toy hauler which is pretty tall but not as tall as some of the commercial loads I move.
I never paid much attention to "truck bypasses" etc until our new 5th wheel, now I do. Had to make a u-turn in the middle of the street in Oklahoma City recently, have to watch low hanging branches in most of the campgrounds, low gas station canopies, etc. Just be aware is my motto, enjoy!
You could put the "Co-pilot" on the hood of the TV with a stick that measures higher than the height of the 5th wheel. If the top of the stick hits something before you get to it, STOP! That will protect you. If you can't do that, just go and watch for the obviously low items as you drive.
The ONLY place I have been where I could not take my MH or trailer was in So. Dakota on the road to Mt. Rushmore from Keystone ( I think ). It was just a very small tunnel carved in the mountain.
Frank
Know your height. Not what it says in the brochure, but what you measured when hooked up to your TV. Mine was actually a few inches higher.
Pay attention. Watch where you are going. Most stuff you need to go under has the height marked on it. But if you are not sure, don't grit your teeth and hang on. Get out and check. Might take longer, but you won't have to deal with a repair bill.
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That will protect you. If you can't do that, just go and watch for the obviously low items as you drive. 
