Another thing I just noticed is that the Rental category is still present in the side widget when on the default Shop page. It occurs to me that the easiest solution would be to simply remove the Add To Cart from all products in the Rental category. Is that possible?
Thanks for the reply!
So this sort of works, but there are a couple of bugs. First, the products display quite poorly. See here: http://test.fantasyattic.com/wordpress/?page_id=265.
Secondly, on the product pages, I still need to replace the Add to Cart button with a Request a Rental button that opens an email form.