Jtom, I have a different perspective after reading about your adventure at Del Rio.
As you said, it is CARGO. As an RP you are allowed to bring into Mexico up to $300USD's of cargo tax free by land. Over $3000USD you need a broker to process the import. I am sure the camper and its contents are valued greatly above that. The Aduana agent should have sent you to a customs broker for you to import your camper and collect the TAXES. Just like Chris importing his TT years back.
The camper has successfully been smuggled into the country.
I am not judging you. I am an RP looking for the Mexican plated diesel truck, get my camper or TT in the USA, and be able to legally go down the road anywhere with my Mexican RV.
I think Chris’s situation is different. I am pretty sure there is some obscure Aduana law stating reporting any improvements on your vehicle. There always is some obscure law somewhere.
You are driving, approaching the border, coming home to Mexico. You have a choice, Declare or No Declare. What do you chose??????? Do you open the can of worms?