Maybe there's a little too much snark flowing in this thread. Though as a non-mod, I guess I could be correctly told to shut my gob.
On topic, now. Straw_Man, does shrink item also shrink the stuff inside the wagon?
Howzabout something like stone shape to hold it in place while you're in a long dungeon crawl? Wall of stone could do the same thing. Invest in an Immovable Rod and make it a part of your wagon; you've got a pretty effective 'emergency-brake', as long as the command word is obscured, say nystul's magic aura on the rod to hide it's magic. That's pretty high level; leaving 5k on 'security' is kinda spendy.
How do you seal the wagon from pilfering?
Too bad a Stone of Alarm is only audible. Heh, car alarm. Could the wagon be put into a rope trick although it's not a creature? Extend it, if so. Maybe make a custom item of it?
Also, although a wagon may not be the most efficient method of holding your extra gear; it's very iconic IMO. And there are other reasons you need to guard or find mundane stuff. For example what if you need to guard a carriage transporting people. Or are part of a caravan train and one of the caravans gets lost.
Plus, I'm guilty of failing to follow 'read, then post.' ubernoob actually suggested track first, but I missed it.