I know I'm not answering your question, but what about the IKEA plastic peg board?
I had thought I'd have to overcome a similar challenge to yours, but in the end we've decided to knock down 2 old outbuildings and replace with something brand new that will be watertight, insulated, etc.
IKEA will be heavily proprietary. There are loads of metal panel options around and most will have the standard 1" hole spacing, for which you can buy masses of accessories on ebay.
I know I'm not answering your question, but what about the IKEA plastic peg board?
I had thought I'd have to overcome a similar challenge to yours, but in the end we've decided to knock down 2 old outbuildings and replace with something brand new that will be watertight, insulated, etc.