Furniture, Wood and Cabinetry Finishing - Hard protective coating for my project

I have just finished making decorative panels for my entry closet doors. I used 12" decorative ceiling tiles with 1" wood trim and want to provide a harder protective finish. They are painted with white latex paint that I don't want to turn yellow.
I'm afraid of the urethenes and am tempted to use several coats of a decoupage medium for them.
Does anyone have any other better suggestions?

The decoupage acrylic will yellow in time. You may want to try a "water white" lacquer...

"water white" is just a marketing term that means when you open the can, the finish is milky in color. it does not mean the finish will not yellow. You would need to find something that states it is Non-Yellowing.

I am always leery of putting a catalyzed finish over a latex product. the finish is much more ridged and could crack with the movement of the latex. Furthermore, many catalyzed products will lift the existing latex. (I am talking about catalyzed because you want a hard film). One of the few exceptions you could try would be a catalyzed waterborne lacquer. These MAY work, but you MUST test them first.

Thank you to the two that responded to my dilema.
I am just worried that since they are just fiber tiles that they could possibly get more than a ding, maybe more like a chunk if I don't try something to harden them.
Thank you for telling me that the decoupage glue will eventually yellow.

I think that I will research a brush on laminate regardless of the time factor.

I would use a waterborne poly. It gets you the hardness without the yellowing.