I had to do a double take the other day seeing a rather interesting/ creative rig leaving the parking lot of Publix in Thomasville, GA. It appeared to be an older HD softail, not sure. To convert it to a most utilitarian trike or in this case "quadra-ped", the owner basically used a small 4 x 6 utility trailer like you would buy at Lowe's had a slot cut out of the center section for the *** end of the bike to nest into and in some way attached it to the frame of the bike. The trailer's tires were aligned with the rear wheel of the bike acting as "outriggers". Not only does this set up give it a suedo trike setup, you can strap on a lot of baggage to the bed of the trailer. Dang I wish I had been able to get a picture. Might even get a small lawn mower on the back. I'm keeping an eye out so if I see it again, I'll try to post a picture.

 

I had seen a picture of what your talking about on line a while back. Also I think I saw another one before that with a sportster. maybe the one you saw. that guy got the idea fromn the first one I saw. Either way. I like what I built much much more.