You can go with tarps (I went through one a year - didn't matter plastic or canvas. You can also buy one that is close online and it'll last a few years (watch out for sharp corners like the windshield area).
Finally I gave up an called a local boat cover guy. It's all custom, all the stress points are double or triple layered. I got 10-11 years out of the one I had made for my 230. I still have the custom one for my 170 and it's in great shape.
