I lay a 2x4x16 across the bow seat to the top of the engine as a ridge, then use a silver tarp tied off to the trailer in several places. It's strong, waterproof, and snow usually slides off of it.
I lay a moving blanket across the console or other areas that could cut or damage the tarp, and they last for 2 or 3 seasons, usually, unless a tree branch falls and punctures them. IF so, duct tape on both sides can do a temp fix.
I like the 10x20 carports, too, but they get destroyed by snow, and I'm tired or replacing them.