PA39, you haven't an argument at all for overloading in this type of operation. Ferry and Air Work.....very different kettles of fish. If one needs to do this as standard operation, the aircraft is not suited to the task.
Whilst structurally one shouldn't compromise the wing integrity by loading extra fuel, many other factors come into play.
Neville, additional fuel (wing supported) should actually decrease spar loads, ever asked the question as to why tip tanks?
That said, rules and limitations are just that. Dispensations (as you state PA39), are just that, TEMPORARY!!
