Poncho or what?

Splash deck
If your concern is keeping the cockpit dry look for a splash deck aka half skirt. It’s like a spray skirt that only covers the cockpit in front of you and does not attach to your body.

Great for keeping pale legs in the shade too.

rain gear
Splash pants, splash shirt, depending on where you live these should be enough to keep you warm and dry - dress for the water not the weather.