The sunlight will break down the product slowly over time. I have seen some that started cracking after just a few years out in the sun.
I think one of the guys had a 12 volt water proof light inside his water tank that made the whole thing light up at nite, it looked good.
U-bolts, straps, blocks of wood all around the totes are good ideas as I don't think that they are designed to be secured in place as they are made mostly for shipping and being stored in place, not really designed for mounting onto vehicles or trailers.
I agree, you can get them used for about $50.00 so when they break or crack just get another one.
I would not store chemicals in them, they are rated for only certain chemicals due to their thickness, design, seals in bottom valve, etc..... I would only use them for water and would buy regular tanks for storing chemicals on the truck or trailer as the tanks are a lot thicker and you can secure them better.
Just my opinion.