How to match indoor audio to outdoor audio clip

There is a reason good sound people always record several seconds of "room sound" ... sound with nothing going on, just the local ambient sound ... as that is a small but crucial part of being able to then deal with things like re-creating comments later via voiceover.

So ... so you have any 'room tone' of the outdoor clip you are trying to match to? Preferably 2-3 seconds of just ambient audio? As then you could create a long enough piece but cutting it into a few bits and randomly grabbing them and dropping them in a track to create the length of sound needed. 

That might help.

Try the Ess Soundpanel or Audition.