We were visited by our regular local demonstrator Liz, who showed us various examples of double bed racking.
Many people have replaced their ribbers with a garter carriage, but you do need to have a ribber in order to rack.
Racking does give a bias, so unless this is what you want, remember to rack in both directions. The grey collar in the photos below were knitted on the bias to allow it to fold easily.
As you will be using yours left hand to do the racking, this can become tender so make sure you take rest breaks and invest in a pair of gloves. Screwfix sell inexpensive lightweight gloves which still allow you to feel what your doing. Right handers will find it more tiring than left handers.
Tension swatches are very important.
The main thing is to experiment and have fun!