I have double 12" rollers on the back that pivot, and on the front, wide flat pads (that also pivot) that allow room for telescoping the boat in and out. The trailer crossbars are telescopic, although I rarely telescoped the boat. A semi-truck load bar with lever handle jacks (phttp://www.uline.com/BL_3888/Load-Bars ... 5QodNWRl5g
) puts enough pressure hull to hull to allow getting the tapered bolts in and out without fumbling with the tramp.
On the front I have an A-frame that pivots on the front crossbar to act as a gin-pole to pull the mast up. I use a couple of trap wires to pull the mast up, leaving the forestay free to attach and unattach. Clip a carabiner onto the trap wires, and a winch on the front mast stand pulls the mast up. It's still a two person job with this setup, as one person is needed on the tramp to keep the mast from swinging about as it goes up. Requires very little effort though, as the mast rolls back into position on the rear mast carrier urethane bow roller. It easily puts enough tension on the rig to not have to worry about adjusting the shrouds with the mainsheet and traveler as is normally done. You just leave the rigging like you want it, and only attach, and unattach, the forestay to the adjuster in the furler. Furled jib stays on in furled position, and is trailered and stored with a pvc pipe slipped over it. The a-frame travels with the peak resting against the front mast carrier, and has the right length line permanently attached so it's easy to clip onto the trap wires.
The trailer also has an upper modular system for double decking another 21, Tandem axles, and is hot dip galvanized. The rear mast carrier easily detaches and has a horizontal carrier for after the mast is up-also have a double front and rear mast carrier that can be swapped out when needed.
I built this trailer in 1988. It went all over the country during the Prosail circuit, and is still as good as the day I put it together when I got all the parts back from the galvanizing plant.
If I had it to do over again, I can't think of anything I would change on it. With this setup, rigging the 21 doesn't take any more time to amount to anything than rigging a 16.