[Pinecone]

Would welding the doors shut increase the torsional rigidity of the body? Hmm, this may be the cheapest mod yet....

Yes, that's why they do it in racing classes that allow it.

Funny thing is also that a race prepped sunroof car is more rigid than a non-sunroof car. The reason is, the sunroof cars have additional roof structure to make up for the hole. When you weld in piece to close the hole, you get all the rigidity of a non-sunroof car, PLUS the added structure put in by the factory.

So, if allowed, weld the doors shut, and weld a panel in the sun roof hole.