dtm is the way to go it lasts just as long as the expensive stuff that you can buy at any marine store and you can get it at your local hardware store dtm=direct to metal. save your money for more expensive parts you may need in the future.
Do a web search for interlux. They have a search engine for their dealers. It will be way cheaper to buy online from a yacht or boat yard than from west marine. Shipping will be a little slow, because paint has to be shipped by ground. Usually about a week. Boat paints require special reducers, so it might be best to call one of their suppliers to make sure you get everything you need.
any marine supply store that sells Pettit or Interlux will work.......West Marine is the Home Depot of marine stores there MUST be one near you! Aluminum is tricky...read the can's directions for alum and follow them exactly....my experience is zinc chromate is the best primer for aluminum, and whatever you do DON'T put copper based anti fouling paint on the bottom......even in fresh water it will eat holes in no time!