You can't say that with legal certainty. Most who claim this ardently want to believe he is natural born because they themselves were born abroad to parents in the military, or their children were. Several attempts at altering the very Constitutional eligibility requirement at question have been made in the form of Bills over the past decades, for the very reason of making children born abroad of military parents eligible for the Presidency. Such an undertaking would have been totally unnecessary if what you claim to be true, actually were true.
I've seen very persuasive arguments that McCain was not in fact eligible, from Gabriel Chin and Lawrence Solum, two very credible authorities upon Constitutional law. I won't go so far as to say point blank that McCain was not and is not eligible, but there clearly are questions. The Panama Canal Zone was leased and was not US sovereign territory. There is some question as to whether McCain was born in the Zone or not, even so. McCain's very citizenship was at question up until the 1952 McCarran-Walter Act, according again to some credible authorities.
It's far from cut and dried, no matter how badly you want it to be.
§ 217. Children born in the armies of the state.
For the same reasons also, children born out of the country, in the armies of the state, or in the house of its minister at a foreign court, are reputed born in the country; for a citizen who is absent with his family, on the service of the state, but still dependent on it, and subject to its jurisdiction, cannot be considered as having quitted its territory.