I am wagon master on a commercial caravan this Fall, I PM'ed you about it. It requires good foreknowledge of the route and its hazards as well as road conditions. As John & Angela mentioned you can do it on your own. The benefits of a caravan the first time is to get your feet wet, learn the paperwork involved, get over the fear factor, & find out where it is OK to take an RV. It also makes it easier to visit a lot of places that are tough with an RV. Most Mexican attractions do not have RV parking lots and are easier with a tour. Places like the Monarch Butterfly Reserve is not particularly safe right now (property crime is the issue)as there are problems in Michoacan state and you should travel with a caravan or another sort of group in parts of that State.
As far as getting a group together you really need to know what you are doing and where you are going and have somebody who can handle Spanish adequately. Especially if you have never taken an RV into Mexico before. It is very easy to become trapped in Mexico with a rig, be it in a small town with narrow streets, archways, one way dead end streets & low trees if you do not have the route mapped out ahead of time. Not so bad with a small motor home or Truck Camper, but a big problem with any sort of trailer. I have led ad hoc caravans down there in the past and it takes a lot of skill to hold more than about 5 rigs together. That is the reason commercial caravans have tail gunners who know the route, or in our case we use the Green Angels who are also mechanics. The point is you have to know the route, you do not want to be stuck after dark looking for an RV park, or arrive & find it full with a 35 rig French Canadian caravan.
Trek America does Central America. Caravans of any sort are a hard sell to Americans in particular. they are extremely popular in Quebec, but the language barrier tends to keep people in groups. If you are thinking of doing this as a commercial venture you have to realize there is a lot of overhead. You can also run afoul of the Mexican authorities if you are not licensed to lead tours in Mexico, even find yourself in Jail. It is Ok if you are not charging, but a soon as you charge you are working illegally in Mexico.