[Nymrod121]

Thanks for your honest and candid feedback. It all comes down to quality, cost and time ... good enough will have to be good enough for the next ten years. In theory, the local water board could come along and insist upon it being moved in order to undertake mains drainage remedial work so perhaps it's best not to build anything that's seriously heavy-duty as it probably wouldn't survive being dismantled!
I'm reasonably comfortable with what I've got in terms of functionality vs. outlay.
Best wishes
Guy