Why protect it if you have to replace? Nothing known to mankind, that would be legal to do, will keep the sun from degrading the paint/ink. It's about $1.25 per year for a new plate. $10/8 yrs. Something with UV protection may help a little. But may react to the paint or cause more fade or as said, yellow. I would just not worry about it and drive on. Respectfully, Sir.
