i would of thaught it can be done via the npc using checkdays for the time period of rental, and login act + name lists to get the items off the char but if the items are in storage i dont know how the server would retreve them
im pretty sure it could be done but not 100% and i dont know exactly how but i think the files i have mentioned would be the way to do it.
you would need to do alot of scripting ppl on here are the dogs at scripts someone must have an idea.