If you have a Morrisons near you get down ther and purchase 8 plastic flower buckets for 99p, cut the bottoms off, use your grow bags as per last year but when you cut the holes in the bag make them big enough to sit the bottom of the plastic bucket in plant your toms into the grow bag. as the plants grow you fill up the buckets with additional compost till eventually the bucket is full to the top. It will encourage more root growth as you fill up the bucket which in turn gives a healthier plant. You also have a lot more compost to hold water. You can also, when you cut the bottom off, cut the bottom 3 inches to look like the top of the wall on a fort. That way you can put the bucket well into the grow bag but the roots will still have access to the compost in the grow bag. Hope all that makes sense. I think you can buy special pots to do it and I believe the technical name is ring culture but Im not sure.

Ian