Those can be installed with rivets or self taping screws.

Those need access from the inside to thread a bolt onto them. But they look nicer

Most boats have those mushrooms on the rear beam. Lots of Stealth have them on the top of the hulls so the trampoline is slid into the groove on the front beam and then laced around.

The links are to the Marstrom shop, but you should be able to get your favorite local merchant to order them.