I have a very similar boat as you but older, 17’ Kellahan cc with a 115 Yamaha. We have no top on ours either. I barely ever use the boat but I’ve been caught in the rain a couple times and I think the ultimate would be an aluminum framed top with fabric over it to keep the weight down like the picture above. The other thing that would be nice is a real glass windshield with a single wiper mounted in the top Center of the window. Just something to think about if you ever decide to go that route.