To clean rust stains of the hull i borrowed a trick from Shannon Lush book on cleaning - use a mixture of Glycerine and Baby powder, make this into a past and use a bit of elbow grease to rub it into the rust stain area then wipe of with a wet rag.
This takes a little time but really cleans the rust stain off well. If any one has a solution for the rust stain from Re appearing i would love to hear it. I have the bolts that hold the front crossbar on rusting onto the hull again, cleaned last year, time to do it again. 
Let us know how you get on
River Rat Perth W.A