The main problems:
I use a shell company to buy my own debt
The only way this could ever happen is if you sold the car subject to a debt owed to a third party and the third party (usually a bank or finance company) agrees to sell you the debt, which is unlikely.
My shell company sues me for conveying the car to conceal it from
This would fail because you had notice of the sale and the knowledge you had is inputed to the entity owned by you. Therefore, it wouldn't constitute concealment.
Also, you would have to join the new owner of the car as a necessary party to the lawsuit and the new owner would have the defense that the new owner is the person in title to the car and had either assumed the loan, or that you had a duty to pay off the car loan upon the transfer and failed to do so, causing the debt to be owed by you and any debt owed by the new buyer to be setoff against it.
Because the new owner is a necessary party, you can't just settle the case. If the new owner isn't a party, then an order to seize the car isn't effective against the new owner because the court didn't have jurisdiction over the new owner and hence doesn't have jurisdiction over the car.
If the new owner was a bona fide purchaser for value and the debt wasn't shown on the car title, then the lender can't sue the new owner.
The shell company now gets a court order to seize the car
This is only possible if the creditor has a right to seize the car because the debt is in default because the new owner didn't comply with the loan terms. If the car loan had a due on sales clause, then the creditor would have had a right to foreclose, but you would probably be barred from doing so.
Even then, it is pretty much impossible to see how you would prevail in the lawsuit under defenses such as "unclean hands".