The bonnets have been rubbing the cowls, metal on metal, on most cars for many years.  The best solution I have found is to place a small self-adhesive felt spacer from your local DIY store to the underside of the bonnet contact area to soak up the grief.
 
Protecting the Paint at the Bonnet Corners II
by John H. Sheally II

I have always used the triangular rubber bonnet tips and like them quite well. They stop the rub and they also keep the bonnet halves from slipping back and forth. I put a bit of clear RTV in them before I slip them in place on the bonnet corners.

It should be noted that these rubber tips were also standard on my 1939 ton and 1/2 Chevrolet truck.
What goes around comes around.