We had a little dolly for moving travel trailer around in the showrooom, but that's about all it was good for. It was pretty much useless on our 1,000' long unlevel parking lot and for 5th wheels. Sure was a bear getting a tandem axle trailer to turn using that dolly.
That's like my first job at a marina - the showroom was quite narrow and to make the cut in with bigger boats the much smaller turning radius of a tractor was awesome, often times with the tractor just barely scraping the far door post to make the boat pivot tight enough to get it near the walls.
We had a B6200 4 wheel Kubota which was about as small as you could get and still have enough juice to move those trailers around - the owner had one of the trailer guys remove the FEL and make a bracket that took the 5th wheel at the top, took regular balls down below, and had 2 big swiveling casters like tail wheels from a rotary cutter. That way you could put some of the weight of the trailer on the ground and get traction/take it off the front axle. Same in the back only it was a 3 point weight bracket with a caster underneath - you'd lift the 3PH to get more traction and lower it to get the front wheels down on the ground.
That thing got worked hard, worst part was that this marina was on a pretty big lake, plenty of large offshore type boats stored there and lots of those owners participated in a program where the marina stored your boat on the trailer, but if you called we had 1 hour to have it launched, fueled and ready to use. Of course that meant people would call on days when the shop truck was out on the road and you would be launching 40' 10,000 boat using a 1200 lb tractor. You really couldn't "brake" that load on the ramp or it would just pull you back into the water until the boat started to float, so we'd put a good long bow line on it, line up and go for it, once the boat started to float off the trailer you'd hit the brake set the parking jump off and start hauling on the rope to keep the boat from floating back into the mooring pier. The guy on board would hopefully get it fired up and be able to take it away but occasionally you'd have a no-start. Fun times.
That thing had full ballast, wheel weights, a rear and front weight bracket. Probably 1200 pounds of tractor and 600 pounds of ballast.