Use an acrylic urethane. This will be a "water clear" finish that won't yellow or amber over time; plus it is easy to apply, dries fast and low VOC. Coronado Aqua-Plastic is the best I have used but Varethane and Deft also make good finishes. I think Sherwin Williams and Benjamin Moore also has an acrylic urethane. Check with your local paint store for availability.