Speaking as a licensed auto/motorcycle/truck/RV dealer, from the info in the OP, the bank owns the camper.
They are the first lien holder, end of story.
For anything to happen regarding the camper they will have to be paid off.
At this point, as posted above, your only recourse is to sue him for the work/services/product your company has provided.
Should be an easy win IF you have supporting documents.
...actually getting any money out of him is another story.
Wish you good luck.