I have had alot of success with two products that are very affordable. Both have very good UV resistance and look great for a very long time. Omni has a single stage urethane and so does Martin Senior from NAPA. A lot of different opinions out there but, I have many years experience in using a wide variety of products.
The flattened clear coat process I read about hear seams to be a waste of good materials. Flattener directly effects the UV resistance of all paints, so why waste good clear coat when a single stage paint will give you the same protection with less materials and less steps in the refinishing process.