I'm planning on going bike touring in S.East Asia. I've been planning which bike to get.

Companies like Thorn offer custom made bikes (specially designed for adventure-style cycle touring), but they somewhat expensive and I have enough expertise to build something similar myself.

I was thinking to use a mountain bike frame because they are designed to take more abuse than road bikes and I plan to ride on rough tracks.

A mountain bike seems to offer much of the ruggedness offered by a custom made bike, but then not being a bike designer there must be some shortcoming using it to carry luggage and over long distances.