Sigma 10-20 + Pentax 16-50 + 50-135 like mentioned above
Or alternatively Tamron 17-50 + Sigma 50-150 (cheaper and non-SDM)
Alot of people find that with their 50-135, FA 50's utility is highly reduced. Can't comment on this since my FA 50 cannot be reduced further in utility

(Not a knock to the lens quality, just its focal length)
If you're going to Nepal, I would think that big zoomage might be nice for long distance landscape stuff...
Another thing you shoudl consider is a small second body like a K100d or K-m. Not having to change lenses while travelling is awesome