Agree with "assume nothing", but with that said I've never had a problem nor seen a situation where it wasn't obvious. Regardless, I watch heights on the road and off the road closely and if in doubt would stop and proceed very slowly with a spotter to ensure I didn't ruin my day.
Off topic - now have a residential fridge so it doesn't apply to me but prior trailers I traveled many many times with fridge on propane without worrying about shutting off to fill up with gas (as I'm sure most do). Is this just a "theoretical" issue? Is everyone just getting lucky, or has anyone actually had a real problem with this?