I was going to ask the same about what to put into the frame. I have used Waxoil on classic cars but was wondering if its a little thick?
Remove as much rust as you can see with a little piece of fine sandpaper. Always extend the area as there will generally be some more under thw paint. I then use something like Krust which is supposed to 'convert' the rust, not sure how. If I can't be bothered to mask the are off or if it's too small to bother with I will spray a little primer onto a piece of cardboard and apply it with a small brush in a 9 to 3 'o clock direction. Let it dry and repeat in the 12 to 6 'o clock direction. Repeat with the topcoat and when dry carefully spray some lacquer over the repair.
