Thanks very much for all the advice. I will get a pot of fuel proofer and do that first as advised. Regards the installation when you mention formers I take it you mean effectively creating a front and back for the tank to sit on. I am thinking i might also put a stick of balsa across the opening to stop any movement from front to back of the tank. This stick would be easily removable should the tank require to be removed.
Does that sound sensible ?
Thanks