Car Modification

My husband likes doing things to cars, and he is getting a little tired of doing things to his own and wants to do things to mine. The problem is, I used to let him with my other car, but this is my first super nice car, and I don't want anyone but a dealer touching it.
He really has an itch, and to be truthful he's good at what he does. When in high school many years back he actually had a business fabricating custom car parts.
Also, he pays for my car. It was a gift from him, but I don't feel this should factor into the decision.
Anyways, he isn't being mean about it or anything, but I don't want to be a bitch.

I mean if its his car.... I wouldn't start to take possession over it (not letting him because you don't want it). just be like I like the car teh way it is... but if you reallllyyyyy want to...

It's my car. In all honesty there are a few things I think would be cool, I just don't want him to take over my car, and I'm worried that anything he does may ruin the warrantee, even if he doesn't hurt the car. I also wouldn't mind if it was just cosmetic, like if he wanted attractive 5 point harness I would be happy; however, he does stuff with engines and tires and brakes, I'm nervous something will break.

well I mean you have talked about it? does he know that? Just tell him your concerned and get him to reassure your safety or something.

He doesn't push me, but he is always looking up stuff he can do and makes it well known about his desires to modify. I think he feels hurt that I don't completely trust him not to hurt my car.

well I guess I would too a little, you are basically telling him that you dont trust his abilities.