Bought the 760LMT a few weeks ago. I took the recommendation of a few on these boards not so much because they liked it as much as they were not happy with the Rand McNally compliment.
All in all it is your typical Garmin GPS with added POIs and profiles for your MH (width, height, weight, etc..) I also have a 40' DP.
When I first got it I took it out for a spin in my car. Was very surprised at the lack of data for bridge clearances. That's the main reason I bought it. Drove it over 4 lane roads and major routes and I got a message "Road not Verified" message, meaning you are on your own.
When looking at what it covers, I see only major highways and very busy secondary roads. Not worried about the bridge clearances on interstates!
I bought a list from LowClerances.com and that certainly augmented the 760LMT but no where near what I expect. So, bottom line, after much research the 760LMT+Lowclearances.com+Newmar Navigation+Rand McNally Motor Carriers Road Atlas+Garmin Base camp download (free)is the very best anyone can do!
Plan your routes, use Base Camp, Garmin and the Atlas for planning the point to point long haul parts, then rely in the Garmin and internal Navigation (if you have it) as well as reasonable judgement on secondary roads. Watch signs, subtract 6" from clearance posted signs for good measure.
Good luck, Mike