Flaming Gorge Lodge will rent flat bed trailers, they also used to provide a 'trailer shuttle' to get rigged boats to the put-in.
The put-in at the dam is very busy in the mornings. Between the hours of 8:00 and 10:00 while the commercial guides are launching they want boats on and off the ramp in about 3 minutes. Seriously. The ramp is 4 lanes and there is barely enough room to manuver a U turn, so NO PARKING at the ramp. They usualy post a ranger down there to direct traffic.
There is pull out area a few hundred feet above the ramp for prepping boats and getting ready to launch. The idea is to have everything ready to launch BEFORE you make the drive down to the dam. The pro's can launch a boat and drive off the ramp in well under 1 minute. The last thing they want to see is half the boat ramp blocked with someones gear and a boat being rigged.
However, if you show up at the ramp in the afternoon you will most likely have it to your self and have all the time and room you need to rig a boat.
Check with the ranger, but they usually are relaxed about the rules after the morning rush.
The Little Hole put-in (11 mles below the dam) it much larger, it has several mutliple lane boat ramps and ample parking near the ramp. What some of my friends like to do is leave a car packed with camping gear at Little Little Hole, launch an empty boat at the dam. Then float to Little Hole and load up. There is no camping between the Dam and Lilltle Hole, so why carry all the gear?