Ah, a quick visit to your site made things much clearer! 230 rolls is more my thing, plus a sensible kit to boot! I was thinking somehow you were far less serious about your photography, hence I suggested -ahem- maybe 40 rolls instead of 20 for your Mongolia leg? forget that-things are clear now.
However, if you still can, by all means try to include some Velvia, even if you have to trade some Sensia 100 or Provia 100 for it. It's worth it, and it's like candy inside that Horizon panoramic!
I have no bad experiences mailing film, probably because I've never done it! lately the chances of film being fogged by security x-ray machines is increasing due to stricter terrorist controls at airports, so I try to carry it with me, show up early and request hand inspections. Yes, I know you're riding and not flying, but your film will fly repeatedly. I suggest you talk to a major courier company (UPS or DHL) and let them advise you. Make sure you get to speak to some knowledgeable person and not a brainless operator.
[This message has been edited by Photog Rob (edited 30 May 2001).]