I have been using the Hullaport for a long time. I am actually on my third set, and when I got my most recent set, I realized they made a design change.
Here is an old Hullaport:
As you can see this hullaport, is curved on both top and bottom. Simple. Classic. Easy to strap a boat too, should you choose to do it that way... You shouldn't but many do. Here is the new one: