Unless you plan to load it and just let it sit I'd install whatever tie down/cargo management system(s) you like, find some stackable storage boxes you like and put your gear in the boxes. It allows you to use the trailer as a normal trailer, which is far, far more likely to be the case, then if need be you can quickly load and secure your gear inside. Just take into account your actual weight and get an appropriately sprung trailer; rolling a loaded toolbox, cases of canned food, a bunch of ammo, etc. into a trailer adds up quickly.
Whatever you get, I'd upgrade the locks if needed, add a rooftop vent if it doesn't have one, add LED lighting and make sure you have a spare tire (bonus points if you get hubs that match your tow vehicle's pattern so that you can swap tires if needed). If you plan to sleep in it, I'd add insulation (I'd actually do that anyways), the vent would be powered such as a Fantastic and I'd add some red LEDs to preserve my night vision. I'd add an awning on at least one side to provide a work/rest area and a fold down or attachable sideboard to work/cook on.