As he says, Martin's the guy to speak to if you're having problems with getting emails through to Doug.
I find that calling Doug is the easiest way to get hold of him. It's rare to get through to him first time, but if you leave a message he generally gets back to you within a few days.
Just remember that he prioritises building guitars over answering emails, which is fairly comforting since you know that when he's working on your guitar, he'll be giving it all his attention. :)