I put in two all of the time. 2003 Ford F-150, styleside bed. I load them myself using the engine and first gear but walking on the bike's left, kickstand and shifter side.
I have a double wide ramp and load the right one first, placing the front tire in the grooves in the bed, using the grooves to help stability, like wheel chocks. I use Canyon Dancers on the bars and one tie down on the right to the bed's tie point in the lower front corner and the left one forward to the lip on the bed, looping it in a "U" through the Canyon Dancer loop and hooking both ends of the tie down to the bed. Tie the front of the bike in its final position, upright with the tubes compressed about half travel. If necessary, now bounce the rear over to the right to final position.
Loading the second bike, I still walk up the ramp to bike's left, driving the bike up the ramp's right, but as I get to the top, turn it to clear the first bike getting the front wheel positioned in the bed grooves. The rear will still be angled to the right. This allows room for the side stand to be used until the front is tied and the bike is upright. Tie the front in the same style as the first (but reverse tie points) then bounce the rear over left after the front is tied.
At the rear, I then run a tie down from each of the bed's two rear tie brackets up to the respective bike's nearest rear peg mount bracket and pull it down. That's one for each bike.
Then, I run a second tie down from each of those same rear bed tie points, up and through the rear peg bracket of each of the nearest bikes, through the opposite peg bracket and on to the second bike's untied peg bracket. Pull each tight as the second, opposing tie for each bike. It has both bikes tied at four points so that the loss of any one tie on a bike won't cause the bike to tip.
On mine, the rear gate just closes, actually contacting the rear tire of the longest wheelbase bike. If yours is any shorter or the bike any longer, the rear gate may have to be left down. The ramp folds in half and slides up the middle laying flat, just fitting between the two bike's tires.
Hope that description's useable. It's hard to verbally describe what's easy to understand if you saw it done.
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