I have a crossover with 20 hours on it. It has what looks like rust on it. What can i do to clean it?

The heat does that, and you're not going to stop it from happening short of never running your motor. You can try cleaning them up some with steel wool, but it's going to happen again next time you take the boat out.

Steel wool will only make it worse over time, as the carbon "leaks" to the surface of SS when it gets hot, causing the rust. Steel wool will only expose the carbon more. Just keep it sprayed with WD-40 after each trip out

I used a wire wheel and die grinder on my stock exhaust then painted it with sum high temp header paint. Waitin for the paint to cure for a few days then I'll find out if it was a waste of time or not.

Put wd40 on it. If you put a wire wheel to it every time you see rust it's not gunna last another month. You might not see it but a wire will is taking material off your already thin exhaust

I didn't mean to do it everytime. Mine came in contact with salt water and then had surface rust from sittin up. Cleaned it and painted it to hopefully make it last awhile longer before buyin a new one.