Pick up is between 1pm and 4:30 pm M-F. You go to the office with at least one of your ebay item numbers and the guy there will print out a pick-up sheet. You bring that over to the warehouse next door and one of the forklift guys will set out the cabinet for you. They do not have a loading dock, and if you want the thing loaded, there's a $35 forklift fee (per item, or per 1000 pounds, something like that). If you're hard-headed like me and don't want to pay the forklift fee, first confirm that it is not included in your ebay invoice (you might have to send them an email to get it removed), and they'll move it to a flat piece of concrete in the warehouse. It'll be your job to get it out to and onto your truck. For the 3' ones, I've been able to get a furniture dolly underneath, shimming with 2x4s and other lumber, and then slowly roll it out to my Jeep.
If you have them forklift them, it'll be easy to set them upright in your truck. I don't know if it would be possible to lay one on top of the other, with the handles and hinges protruding out. You could set two on their sides, which is what I did for the one on my Jeep, but I had to use a comealong to slowly tip the thing over and against the bed of my little truck. Rotating the 5' or 6' ones would be a huge job, I think -- and not very safe.
But if your truck could take two of them standing up, they can forklift them up, or you can use a comealong to get them up a ramp. I'm trying to remember how I did my 4' ones on a Home Depot truck, and I think it was just a very slow process with a comealong and helper ropes, and some luck and patience. Stood up, they're pretty table. You could use ratchet ties to hold them together and to secure them to the truck. Just take it easy in the corners, from that point.
If laying them out flat in the truck is the only option, the doors do come off. Just bring some blankets or plywood or something to keep the hinges from cutting into the paint of the next-door-neighbor cabinet. The hardware that holds the shelves uses a 9/16" nut. You can take shelves out and doors off to lighten them, somewhat.
But they're not light. It's something like:
3' = 500lb
4' = 700lb
5' = 9000lb
6' = 1,100lb