Welcome to the forum.
I shoot outdoor typically and sometimes in low light. Let me share my own experience and thoughts. From your description of your needs, I believe that you would be better off with a WR body, preferably the K-7 or K-5 because their body is compact and very solid. (K-7 and K-5 have the same body.)
Low light shooting will always be a challenge with any camera, although the K-5 might be superior at High-ISO. I think that you need to consider directly to buy a fast prime lens: ie, a large aperture lens (or low f) like a f1.4. There are several great fast prime with K-mount incl. the Pentax 50mm lenses (MF f1.2, f1.7) , the FA 50mm (AF f1.4), ... There are even some great lenses like the Carl Zeiss 50mm f1.4, Voigtlander Nokton 58mm f1.4. Since you shoot outdoor, you want a solid lens (not necessarily WR, but with a proven track record).
Based upon my own experience incl. backpacking with my K-7, my favourite setup for such activity is:
- K-7 + DA18-250mm for day time, and
- K-7 + Voigtlander Nokton 58mm f1.4 for dusk, dawn and night time.
I have the K-7 mounted with the relevant lens, and the spare lens in my backpack. The DA18-250mm is a great all-around lens, ideal for daytime. The Voigtlander 58mm f1.4 is a fast prime (MF) that is very robust.
Note: Both the DA18-250mm and Nokton 58mm are not officially WR, but these lenses are very, very sturdy. Many Pentaxians used them outdoor incl. in the rain, snow, and ice, mud, dust...
See also the threads:
https://www.pentaxforums.com/forums/pentax-dslr-discussion/106600-k-7-high-is...gh+iso+success https://www.pentaxforums.com/forums/pentax-dslr-discussion/135851-how-elminat...gh+iso+success https://www.pentaxforums.com/forums/pentax-dslr-discussion/135402-does-k-7-ge...gh+iso+success
Hope of these comments will help...