You will find an RV park at the west end of Lake Chapala, in Roca Azul near Jocotopec.
You can get an FMT for 180 days, no more, but when you do need to get an FM3, you will have only 30 days to change your address with immigration when you move. An RV park receipt should be your proof of address. Be sure to plan the timing when you get an FM3 because you MUST be in Mexico at the same time each year to renew it.
No need to worry about an inventory of your contents in an RV; just don't be carrying new products in boxes that they may interpret as being for resale in Mexico.
Each person may temporarily import one vehicle. A motorhome and a toad are linked on the import documents and must leave together. You may not sell any vehicle or trailer in Mexico; all must, eventually, be removed....no matter what. In other words, you can't tow something in, drop it and then take the vehicle back and tow in something else. That might be a problem if you have only one vehicle capable of towing.
Hope that helps.