Supporting tomatoes in tubs

Hi
We normally put two tomato plants to a tub and stick canes in the ground in the greenhouse to support.  However we now have a lovely greenhouse complete with a floor of weed proof fabric and stones, so are unable to stick the canes in the ground, and the tubs are't that deep enough.  Any ideas on how to support our tomatoes?
Thank you!

I use canes of the appropriate length - the tops are supported by a single length of plastic coated wire stretched along the inside of the roof (the wires are supported by small angled brackets bolted to the channels with crop-headed bolts.) The bottom ends obviously go in the planter/pot/tub or whatever.

You still have to tie the stems to the canes as they grow, so strings could be better, although I don't know how much time you have to spend persuading the stems to wind round them (Mum probably does.)