Funny you brought up this thread as I was just reading from Daniel, in the Septuagint, and noticed a particular usage of entos that shows without a doubt that it means "inside" just as it is used in Luke 17:21.
Daniel 10:16 LXX-Septuagint (Brenton Translation)
16 And, behold, as it were the likeness of a son of man touched my lips; and I opened my mouth, and spoke, and said to him that stood before me, O my lord, at the sight of thee my bowels were turned within me, and I had no strength.
Daniel 10:16
16 και ιδου ως ομοιωσις υιου ανθρωπου ηψατο των χειλεων μου και ηνοιξα το στομα μου και ελαλησα και ειπα προς τον εστωτα εναντιον εμου κυριε εν τη οπτασια σου εστραφη τα εντος μου εν εμοι και ουκ εσχον ισχυν
http://biblehub.com/interlinear/apostolic/daniel/10.htm
εστραφη τα εντος μου εν εμοι - "my insides (inward-parts / bowels) were turned within me"
Luke 17:20-21 KJV
20 And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:
21 Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within [G1787 εντος/entos] you.
Yes, the kingdom of Elohim is εντος-inside-within you.