Gut feeling is integrity of the underlying paint will be much less than the average auto paint.
I'd snaffle another bonnet, get that done as per your plans and when the event is over,keep and hang the art work bonnet somewhere inside and refit the original one back to car.Just swap the bonnets around on special occasions.
The idea is good (in theory) but I don't think in real terms you can get canvas paint stuff adequately protected.Incompatibility and UV would probably kill the artwork quickly.
You could ask around at street art forums what paint combo 'may' work (best) , but I still think the lifespan will be compromised.
Not all acrylics are equal, and auto acrylic does not like being applied too thick.It crazes,lifts and cracks.