I paint all my boats with Krylon, then clear over them with Duplicolor Clear TopCoat... Make SURE it says "TopCoat", and not "ClearCoat" or similiar... I have cans of each and there is a difference... It's Laquer based, so I wouldn't advise it over enamel (found that out the hard way...)... I also would NOT use it over Krylon Fusion paints, especially if you've applied and removed any blue or green or ??? masking tape...... (found that one out the hard way as well :angry: )...
The Duplicolor Clear TopCoat makes the base paint just "Pop" with glossyness, and it seems to hold up well if everything is prepped accordingly...
Try to let the Krylon dry for a decent period of time... a week or better in warm, dry conditions is best... Then let the clear dry for some time as well...