Good Evening and Welcome to the Forum!!!!
The only time I was able to hold the Pentax body before purchase, was almost 10 years ago with the K100D. Otherwise, I just ordered the K20, K5 and 10 days ago the K5IIs, sight unseen/untouched. I have had no worries, and no problems. I do get the Pentax extended warranty for $20 that takes the coverage from 1 year to 3 years in length.
I have been at Philmont several times, back in [you really don't want to know - before the Tooth of Time]. I used my dad's film Kodak 35mm with a 50mm lens. It was smaller and lighter than today's bodies. Personally, there are weight and size are issues, so I would limit myself to the body and the 18-135WR lens, with an extra 2 batteries (3 total), and 2 64GB SD cards. That's it. That will be good for 1800 to 2000 shots. I would also turn off the rear screen in order to extend the battery life. You could squeeze 2K shots on a single SD card (in RAW), but they are light and you will have a spare in case of a failure. The 50-300WR lens would be a luxury - and do you really want to carry the weight? Also, the Pentax OEM batteries have a longer life that the 3rd party ones.
The body - I think that the K5IIs would be perfect. Size and weight count a lot when you are carrying everything. The Rocky Mountain Canaries will carry the tents, cooking gear and the food. You will be carrying everything else - and there are no Sherpas. The K3 is a tad larger. Here is a visual size comparison.
Hope that helps - have a good time....
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Then again, for the ultimate in size and weight - there is the Q-S1...
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One more idea that might be worth the weight. A very small light tripod (Gorillapod or something similar) with the 1oz IR remote. This way, you will not be the guy that goes missing in all the images. A second thought, is that there are going to be some wonderful low light (and I don't mean high ISO) shots in the evening and at night. Moon lit shots of the Sangre de Cristo's is usually something that you probably can't get at home.
Last edited by interested_observer; 12-11-2014 at 04:39 AM.