I have a Coachmen the one with the Dalmatian dog on the logo from 2001 and it is as good as new, the last post is advice for Coachman a different RV all together.
I will recommend taking a small car behind the RV, do not use a big SUV or a Jeep or a pickup truck more like a Kia that can be towed 4 down, this will come in handy since driving in a big RV into some of the old colonial towns and cities will be impossible, Guanajuato is one example another good item to have is a tote to empty the waste tanks, specially in countries further South.
Make a loose itinerary in order to be able to visit some of the museums and archeological sites, the ground floor of the museum of Anthropology in Mexico City takes about one day to see everything, the little one will not want to see it all, the car will come in handy when you have to go shopping or in an emergency and it allows you to be flexible with time spent visiting, as an example you are in Oaxaca and decide to visit the archeological site of Monte Alban, you take the tour bus up the mountain and one of you has a mild bout of Moctezumas revenge, with the car you can go back to the RV and not have to suffer waiting for the tour bus to go down to the city and then take a taxi, in the long run paying for taxis will be expensive.
Do not skimp on insurance for the RV, yes all you need is liability but that will not cover any medical issue that you might encounter, whether it is in Mexico or further South.
Travel advice, DO NOT travel at night in any country plan your routes so that you start in the morning and are at a camp ground by about 16:30 or later, that will give the small ones some time to play, and remember that you need to go slower than what you are used to in the States a good speed for roads is between 55mph and 60 mph anything higher is not advisable, and you have to look out for the famous "TOPES" (speed bumps) a favorite of the gringos, all towns have them and many are not marked at all, when coming upon a town slow down to about 25mph if possible, and get a game going with the kids, "TOPE LOOKOUT"
The experience for the kids will be invaluable, it will open their mind to other cultures an people, they probable will learn not only Spanish but maybe a native language, you never know.
When out and about do not let the kids walk bare foot there are some deceases and mushrooms that can be picked up by the bare feet.
Otherwise have a good trip, buen viaje caminantes.
navegator