I cut the growbags in half - each becomes two big soft 30cm pots.
As a lazy person, I also set up a row of them (crosswise) on a pair of 4x2" timbers: Cover the gap between with thick polythene so it's a trough, push a 15x3cm strip of capillary cloth through the bottom of each 'pot' so it can dangle to the bottom of the trough, fill the trough with water - and neglect for a week or two at a time... You need something to stop them toppling - a loop of rope will do.
Cheers.