Verifying Height?

Ha! I was tempted to post the shadow measuring, multiply by ratio song and dance when I first read the original post! :)

Remember that if the high point is not over your trailer's fulcrum (ours is at the BR vent cover, in front of it) that you've got to allow some extra space. Interstate overpasses are no problem, but an old RR bridge may have a considerable dip right under it that'll catch whatever it is that's highest.

Must not be much to do in Alberta this time of year. :)

I did pretty much the same as many others but had it easy as I replaced the old batwing antenna near the edge with a Jack antenna. Measuring the height made it simple and came in about 12'8". That didn't help when I missed a low hanging brach going into a state park and knocked the jack clean off. Even when things aren't marked we have to watch out.

Don't have a ladder? On a sunny day, park broad side to the sun so the shadow of your A/C can be seen clearly on the ground on a level surface. Measure from the center line of your trailer to the peak of the A/C shadow. Find an item short enough to measure its height (or use a yard stick) and measure it and its shadow. Figure out the angle of the shadow by taking the inverse tangent of the stick height divided by the shadow length. Then simply take the tangent of that angle and multiply it by the length of your trailers shadow. Voila - no ladder needed.

Tie length of brick twine or the like to straight board with level
Level stick across highest point.
Let string hang down to ground.
Have DW mark ground intersection on string with Sharpie.
Climb down off RV and safely measure board to mark with tape measure while on ground.

I have a six-foot level. :)

I am 13' 2". Measured hooked up and with a stick and level like above. I made it under a trestle marked 12'8" though. The underpasses are measured posted at the least clearance. Top of curb at the uphill side in this instance. And in this instance, with the 4" curb and the slope of the road under the trestle I was able to clear, but I did not go fast.

Yep, a straight edge, ladder, level and tape measure - 13' 4" at top of front A/C unit. And I go under a 13' 6" clearance all the time. In the center it is more like 14' - remember it is the minimum measurement posted and that's USUALLY at the edge.

Same as what has been said. Do it while hitched.