Locking Utility Trailer Spare Tire Mount for $5

I need somewhere to mount my spare on my utility trailer. It needs to be out of the way, inconspicuous, secure, and inexpensive. The standby tire mount won't fit on the a-frame as I have a a Harbor Freight tongue box mounted there already. I don't want to put it on the side of the landscape trailer as it will most likely get in my way. Furthermore, I don't want the spare to be out in the open as it can be tempting to thieves thus requiring a lock which adds to the expense. Mounting the spare underneath and running the bolts up through the trailer box satisfies my requirements. Being attached from inside the box keeps it secure when the box is locked, it is somewhat inconspicuous, and it is out of the way.
Mounting it in this fashion requires the fabrication of a simple mount as running bolts up through the wheel and the box from underneath with no support would be difficult. Attaching carriage bolts to the wheel in a rigid fashion to create an assembly where the bolts act like studs held securely and parallel simplifies the act of mounting it up from underneath. The only materials required are two carriage bolts, four wing nuts, four flat washers, and about 6 feet of 1"x2" furring strips.