I'm planning on going bike touring in S.East Asia. I've been thinking about which bike to get, and I've seen companies like Thorn offering custom made jobs, but they are too pricey for me. I was thinking to use a mountain bike, as the frame design is similar. What are the advantages and disadvantages of an mtb frame vs a touring or road frame?

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.