You have it correct. After removing the pins and the 'U' shaped caps the head pulls out. But the rubber damper likes to hold onto the big square shaft so just give a little extra muscle.
Then remove the four pins holding the base to the bed rails and lift. I personally can't lift it out on my own so I get my son in-law to help. As a side note, my base has 4 little rubber spacers, one under each attachment point, which keeps it more quiet. If yours does as well, be sure you don't loose them. Sometimes they stay attached to the base, and sometime they fall off. I just take them off and keep them with the pins till next season.