I would be wary of putting anything on top of the smoothrite now, as It seems to react to other paints (it went all bubbly once when I sprayed over some with a rattle can of something else).
A couple of coats of something clear to protect it would be cool, but given the easy life it will have now I imagine the wax coats should do it.
I have just ordered a tin of that harly wax.

what would be a good polish for the new paint (on the top of the car) to go on before the harly wax?