Re: Which cover if stored in a boat slip for summer?
The properly vented, snap-on, Sunbrella cover that goes over your windshield is going to be the best, but depending on your patience you can use one of those trailer-made covers like I did for two seasons. Goes like this...
Pile the cover in the boat, rolled up so you can unroll it from stern to bow.
Extend the straps that go under the boat to their longest possible length.
Stand at the bow and drop the stern-most strap in the water while holding each end.
Walk it back under the boat to the rear and connect to each rearmost attaching point and snug it down a bit. Unroll the cover a little.
Take the next strap, go back to the bow, drop in and walk it back and attach.
Do the same thing to the next set of attaching points. And the next, and the next, etc., etc., sliding each strap under the boat and attaching while unrolling the cover.
Eventually you will have all straps attached and the cover snugged down.
If the straps are not long enough to allow you to hold both ends at once, attach thin leads to each end. Because your slip is covered you don't have to worry about much rain pooling in the centre of the cover but it is possible to rig a pole system this way too.
Believe me, this is as much of a PITA as it sounds.

But I got by using a $150 cover for two seasons this way before I dropped the required larger cash for the custom snap-on job.