Is an RV GPS necessary?? IMHO no, is it worthwhile?? Yes. in addition to routing help, the Garmin RV760 has campground lists, service facilities, dump stations, etc. etc. that come in handy.
Are they perfect? NO. the biggest issue is that data for routes is often obtained from state DMV. And that can have errors. the biggest one I've noticed is clearance. I've had several cases when it said I was to tall, and I knew I wasn't.. the issue is that the tunnel shows side clearance less than the trailer, but overhead is ok. And going to the state website ALL that was listed in these cases is the tunnel side clearance. overhead wasn't listed.
you can run into the same issue with length since sometimes length restrictions are based on trailer rather than overall length. and the garmin only lets you put in one length, you can choose, overall, or trailer. I wish it would let you put in both.
and with the garmin, the backup camera is IMHO very usefull. wire it up for always on, great for checking clearance when lane changing.
When I'm going somewhere new, I do a route check using online state info and streets and trips etc. to plan a route.
2011 Keystone Outback 295RE
2004 14' bikehauler with full living quarters
2015.5 Denali 4x4 CC/SB Duramax/Allison
2004.5 Silverado 4x4 CC/SB Duramax/Allison passed on to our Son!