Idea for car audio, not sure if feasible, but would like thoughts.

Some of you know that I'm planning on shooting a scene in a car pretty soon. I've decided on shooting the whole thing practically which means that I might have trouble with audio.

One solution that I've considered is this:

Lining the roof of the car above the actor's heads with sound-dampening material, then recording dialogue by booming them from under, thereby preventing the engine sound from being prominent.

I'd like to hear people's thoughts on this solution. Does it make any sense? Is it a good idea?

Thanks.