To simplify the installation a T bar should be made. It will make the layout much easier and it will hold up the cross arm. This will save you from working against the spring tension.
Make the T bar from 3/8" rod, make it to fit the largest hatch opening of the bins you are going to install openers on.
Put the leg of the T bar through the back rail hole and center the to of the T bar with the center of the hole
Mark the holes for the back rails as per the individual instruction.

After the cross arm and springs have been installed you can put the T bar under the cross arm to hold the cross arm up.