RE: securing a location
If I was to wear Daisy's outfit (Even a part of it), this economy would hit it's all time low from shock..
But once ya find an ideal location, mention to the owner you only need to park you cart part time, it goes home with ya, you're only using 60 sq. ft of space, inform him there will be no floating wrappers (you'll clean up afterwards and have trash recepticle(s), and maybe offer to feed him and discount his employees. This is just off the top of my head, since I've yet to deal with this situation. Then you can always maybe offer to put up a rack for the guys sales flyers to help advertise him in return for the rent (or put an ad in every bag that ya fill with food that goes to your customers).. Either way, good luck there!
I should also mention, if you do a search in the Hot Dog Forums, you may find alot more info on this. From a few vendors I've talked to, few of them pay 10% or so of their sales.. Others that set up in locations like Home Depot or Lowes pay around (+/-) 4 figures a month for rent.