Ring culture in the GH

I've never had a GH on soil, always on a hard surface. In fact my first ever GH was on the roof of an extension, accessed through the bedroom window. It was during the big drought of 1976 and I watered the tomatoes with bath water (shared of course) from the bathroom which was also alongside the extension.
The tomatoes were my best ever and there was no problem with slugs or snails. For the record, its GH2, which has been moved 3 times.