The doors can be hard to open but they're as secure as the lock you put on them. Some guys will remove the doors and frame in the end for a regular house type door. It's a lot more convenient. Of course that wouldn't work for storing a UTV.
They can get as hot as 150F and 130 is common. If you store anything that can't take a lot of heat, I suggest putting some kind of shade roof over it. Painting it white will help, too. Another option is installing some vents and a powered vent fan. Make it a big one.

They come in several different sizes. Here's a chart showing some variations. There are also high cube ones that are about a foot taller.
[Linked Image from zirconcontainer.com]

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