I used white rustoleum, rolled on. Looks nice. Wal-Mart sells an oil-base similar to rustoleum under their Color-Place brand that is cheaper. True-Value has X-Orust (sp?) that is similar. I recommend any good oil base for durability due to the heat cycles the interior sheet metal will see when your bus isn't in use. I don't know how well a latex would last, I did however paint my bathroom with Wal-Mart latex, Time will tell how well it holds up.
79 International Wayne