How easy is it to use gold for exchanges?

Consider the case in 1930 when an exchange takes place between a Frenchman and an Italian. If the good exchanged weighed one ounce but the gold exchanged was two ounces of gold, then ultimately one has a problem, shipping costs are three times higher than in a fiat currency!.

As economies diverge we delay gold shipments for small purchases until we enough of a gold deficit to justify a large shipment. There is no way around the problem, so wait and let gold deliveries be pending, and a pending gold shipment is fiat currency by another name. Can central banks use gold for exchanges? Yes, better than retail traders because there are fewer central banks and they can make larger transactions less often, gaining economies when shipping gold.

The best gold economy will be a closed economy sitting on a 20 square mile island. If the economy is reasonably closed, then external gold shipment are rare. Hence my Island Banking proposal. Gold is reserved only for large bets among rich people on a small island.

Why do Keynesians trash gold bugs?
Mainly because Keynes is generally wrong.   Gold bugs use gold as a hedge, not money. And monetary gold advocates often forget:  Once we have the pending gold shipment, then we are shipping risky paper.   

France could be on the gold standard as long as they had a long term legal right to German reparations,  because then they wouldn't have to ship gold around so much to cover short term variations.