As will know by now, we made it back! In the end, it wasn't too bad. Lost keys were covered by the Ford roadside assistance but nobody could get a key cut on a Sunday. As we HAD the RV back on Monday morning, a tow was arranged, Ford covered the call-out charge and the first 35 miles so we ended up paying $130 for the remaining mileage (43 if I remember right). On the plus side it saved us about $50 in fuel and about $32 in mileage on the rental as we were paying $0.40/mile, which brings the cost of the tow down to $50. The rental company got a locksmith on the Monday morning and we paid him directly ($75, instead of the $125 the rental co wanted to charge!) as it wasn't a coded key. On the down side we had to pay $75 to get the tanks emptied, rather than $30 at Sebring if we'd done it ourself and about $65 for the prop-shaft to be re-installed (including new bolts, which had been damaged in removal). All in all it wasn't as bad as we feared.
Woolly.