Bought a boat cover and put my boat outside with boat cover on it. Well it rained last night and somehow the left rear corner of my boat got water in it! How?? It was secure .. there was. A couple gallons that was puddled in center on top cover...
Any cover regardless of quality will pool water unless the cover is properly tented. If so much as a cupful of water can pool on a cover, that pool will continue to build as the cover sags and stretches. At some point the seams can begin to stretch thus allowing water in. It is all about getting the water off the cover.
Silvertip is right. Tent the cover properly and you won't have an issue. My cover has an extendable pole to tent mine for runoff. My old boat had a matching cover from the factory hat fie perfectly so water never sat on it.
On a separate note: you mentioned your boat sits outside, I learned a valuable lesson in boat covers once. In severe hailstorms loosen you cover. We had a hailstorm in Alberta where I used to live. The hail was the size of baseballs. My cover was on but not tight. Most others had theirs tight. The ones that were loose had no damage to their covers. The ones that were tight had holes wherever the hail hit them. My guess is that the loose cover worked kind of like tarmpoline for the hail, instead of like a drum.
Make sure its just tight enough to stay on in the wind but that's about it. Much better to have to drain any water on it later than replace it entirely.
I have a very old cover, & much in need of replacement. I have the same issues with pooling water seeping in when I don't tent the cover. What I ended up doing, although I'm sure you can buy a tent system, was, I was throwing out a broken floor standing fan. It had an adjustable shaft & I cut the fan off & it works perfect for the front or back. I had to make another shaft out of a piece of round wood stock from Lowes for the other end, but super cheap fix.
If your cover isn't a snap on and it's too loose like try hanging milk jugs or weights off the sides. It will keep the cover tight and if you keep a pole or something else underneath you should be good to go.
I'm currently using the milk jug solution on my boat with a trailer cover while she is docked in the water. I didn't feel like spending $500 on a custom snap on canvas. So far so good...pretty dry!
Mine was comming in on bow rail at back under canvas and running in the motor blower intake & exhaust vents I removed to find out how and they aren't sealed where they were cut thru to mount them .
