I use a helper, if i dont have a helper i bring my flat bed trailer with the drop down gate and simply roll it up on the trailer and go.. i have struggled at time when alone and have a surprise emergency install and not have my trailer with me and getting stuff off is easy but back on can be a challenge..
helper or trailer is best but a cheap quick ramp assembly might work but i may not have room in my f250 long bed as its stacked with tool boxes,ladders, and other stuff already.. carrying around a bulky setup for the occasional a lone install might not be worth the trouble for the money etc..
load CU on the plywood in PU bed, towards back of PU bed. Slide plywood out to make a ramp. CU will be attop of ramp. Now slide it to the ground.
To load; slide plywood out to form ramp. muscle CU to bottom of ramp, then push it halfway up the ramp. Not to hard. now lift plywood ramp up and slide into pickup bed. weight will be half of CU weight when CU is halfway on the ramp.
Also, keep lengths of 3/4 or 1" pvc pipe to use as rollers. can be used under plywood or under equipment.
Also, find a good scrap guy that can meet you at the job. they will help unload and load scrap for only the scrap value. Many here that will fight for your business.