Perhaps this will help on general methods, options. Unsure which might be best relative to harsh conditions mentioned and RNA study. In college, many years ago, we used cyanide in kill jar before mounting many types for insect display collection. However, this may not work for RNA need for quick isolation (second link). I don’t know whether capturing and transporting live specimens for analysis would be feasible if freezing isnt possible. Contacting the Zymo Research unit may help determine if their RNA extraction kits could be used in harsh field conditions.