I have a 38' powerquest (1995) when it is covered, and it rains the water will cause black steaks that are next to impossible to wash off. As I wash the water beads up. I have been using 3M products to rub, finish, and wax. The top of the boat rubs out good, but will not last. The entire boat will not hold up with the 3M products, any thoughts???? (sides look better than top)

Have you tried wet sanding and buffing? I use meguiars car wax on my daytona.

If you decide to wet sand go with 1500 then 2000 then buff it will look like new! Then wax it a couple good times.

Don't wet sand it, just buff it. Also lay your cover out and scrub that clean. I had the same problem with my cover and i washed it real good a couple times and then buffed the boat and haven't had a problem since.