Your point of "it all has to do with weight" is incorrect. Regardles of weight, a tandem axle has to be titled and licensed in Oregon.
Utility trailers in Idaho have no titles, just registration slips and plates. Up until last year we could buy a 10 year plate but yearly now.
Seems easy to me keep it under 2000 lbs. From Florida DMV web site. A certificate of title is the proof of ownership to a motor vehicle, mobile home or vessel in Florida. Florida law requires most vehicles to be titled and registered. The exceptions to titling are mopeds, motorized bicycles, and trailers weighing less than 2,000 pounds.
Obviously, you put it on a trailer! I know that States recognize other States registration but if the State you are from doesn't require registration and you take the trailer into a State that does require registration, could it be a problem? I guess I would prefer to have some proof of ownership from a government agency just in case. I like the idea of an inspection so I don't end up hitting something in the road because somebody's home built POS fell apart.
http://www.oregon.gov/ODOT/DMV/contact_us.sh Now im being a dick.... I called the eugene number because you caused just an ounce of doubt, but you were still wrong, it is a weight thing. This is getting a little off topic as we are in a different state as the OP. Im done. Have a nice day.