Hola Familia Contreras!
What I was told by SAT via email is you are supposed to have a temporary import permit for the camper which apparently is a form you fill out they refer to a Anexo 1 which can be found online with instructions at the following address........
http://www.sat.gob.mx/informacion_fiscal/normatividad/Paginas/reglas_comercio_exterior_2017.aspx
Scroll down to......
Annex 1 General Rules of Foreign Trade. (1)
ANEXO 1 DE LAS REGLAS GENERALES DE COMERCIO EXTERIOR PARA 2017
Formatos de Comercio Exterior
Contenido
The first form I think is the one you want "Autorización de importación temporal"
Tip for Barb - hold the left clicker down as you drag the cursor over the entire address above so that it highlights - then with your cursor still on the highlighted address release the left click and press the right click and you will get a window with a few options one of which is GO TO and the address - just click there an go. You may not need this but it is a new thing as of Jan 27, 2017 and was added to laws in Feb 2017. You can read what it says. They told me this is what campers need. I do not know - I am not the authority....
PS - Last time we crossed at Laredo - Columbia - but not Laredo - they put us through a full-on inspection and X-rayed the entire Bus. Things change. You never know.