I have some tumbling tom tomoatoes in troughs (plastic) hanging off the
fence which are flowering but then don't seem to set fruit . The
flower just turns brown and dies off.

However I have another one of these in a hangin basket lined with part
of a compost bag cut to shape , inside out and with holes in.

I did ensure that there was proper drainage etc in the troughs.

Could this just be a watering problem , I do water them everyday ,
could it be because they are in normal multipurpose compost that they
are drying out to quickly and not allowing the fruits to set ?