Trialer Question

I have been looking around awhile at my bike, and how i'm going to mount a motor to it. I was riding it down the road one day and started to think a trailer would be perfect for me. I got on here, looked around, and seen some done ones.

Well, I didn't like those type of trailers, I want a trailer that can haul stuff, more then just the motor. Such as pop, cooler, tent, and so forth. I had a idea for a simple trailer, about 2ft. wide and 3-4ft. long. Mount the motor in the back with the real axle (2 wheels) and it's going to be vertical motor. I was looking at a push mower, and wondering on what I should use.

Anyhow, the basic setup would be with the rear axle, with a sprocket (or what ever it's called from the rear of a stunt bike) attached (welded) onto the axle. Connected the frame to my bike isn't the problem, just not sure what I need.

Why? And I just realized I need a horizontal motor that will sit down under the axle. Going to have it sit about near the middle in a little hole compartment. And i'd rather not spend money, or at least not that much. I got most of the supply's for a frame, and I can acquire more if needed. I don't care on how heavy the frame is, I just need it so I can carry luggage around. I have access to a 3.5 HP , 3 HP, 5 HP, and a 6.5 HP engine. Still not sure on how to do the trailer though.