You will need:
3 tomato plants
First you need to position your growbag, I put mine in a black rectangle tray from Homebase. Then cut out 3 holes around the growpots. They have stakes in the bottom, so just slot them into the growbag. Then put in your plants and canes.
You can keep the outer trough of the growpot full up with water. It takes 4 pints and is great if you are away for the weekend or a bit lazy like me! The inner trough is for your tomorite or other feed. They were £16.99 for 3 pots from Lakeland. There is supposed to be a greater yield, so I'll let you know how I get along.