For reasons already stated (weight, drag, civil clearance), a boom fit for FSTA would be most unwelcome to Air Tanker. If the number of HDU fitted aircraft meets the RAF daily requirement then they could perhaps have a boom and a pod centreline as Beags suggests. The hose on the end of a boom is a very poor third option. As far as one can gather from the limited information available Air Tanker would expect to have a number of frames available each day for their own use unless they have been given a fairly long period of warning. That is the PFI deal.