Decent quality acrylic usually carries a 10-yr warranty against UV-induced hazing or yellowing. That's for outdoor use. Indoors, there should be much, much less UV exposure that it should never happen.
Almost all acrylic aquariums are solvent welded, not "sealed," so the joint is basically indistinguishable from the panels in terms of chemical or physical properties, e.g., it's not more vulnerable to UV than the rest of the acrylic.
Still, I wouldn't store anything valuable outside in the sun if I had a choice. Exposure is generally not good.