I've been researching them too, as I plan on getting an RV-specific unit this year. I have read too many owner complaints about Garmin not helping with questions or problems, and not doing free map updates. I think it now comes down to either the Rand McNally unit, or the TomTom via 1605 (for actually about half the price of the Garmin).
But I have heard that RM and TT may be coming out with an updated unit this summer. Since I'm in no big hurry, I may wait to see if that materializes. Good Sam already had their Rand McNally version on sale last week for $70 off (I think it was on sale for $269.00) They and TT also do 4 free map updates a year for the life of the unit, have a rear port for external camera, and can be set for the type (height,weight) or motorhome you drive.