I've a 2012 plus 8 with a luggage rack that fits as you describe. I have not had a problem, 3,000 miles mostly with the hood down. The brackets and bolts are well recessed but I can see you might if you stuff things tightly behind the seats. I'd get some stick backed foam tape from the dealer.
And I'd add that this is the most spectacularly wonderful sports car I've ever had, and that includes trad morgans and most other sports cards from cheap to luxury over the last 35 years. It just begs to be driven. Plonkers who prefer Porsches are welcome to them.
