For Portland International Airport, I'd avoid carrying even in the non-secure area, just because of Portland's general squeamishness around firearms. Outside Portland, you should be fine. Astoria is the only airport in your county that got scheduled airliner service, and it's both already gone, and was through a 'charter airline' that didn't have you go through FAA security anyway.
It's one of those "it may be legal, but the police will hassle you anyway - so unless you WANT to be the court test case, avoid it" issues.
When I took my Utah (with Oregon addendum) CHL course, it was emphasized that Oregon has no "duty to retreat" OR "stand your ground" law, so it comes entirely down to whether the police and prosecutor decide to charge you or not. But that was at the state level. Locales may not be able to legislate gun RIGHTS, but they can legislate BEHAVIOR with guns (see Portland's "gun crime reduction zone" silliness,) so maybe Clatsop has a "duty to retreat" law?
Lets start by saying that for legal advice, you need to consult a lawyer, and
after relieving you of several hundred dollars, the advice you get will most
likely be something along the lines of "maybe".
On airports - in Oregon, you may carry in the public part of the airport, but
not into or beyond the security checks.
The advice on when you can use deadly force is correct.
I suggest that you go online ans spend some time reading section 161 of the Oregon
statutes.
Basically, you can use deadly force to prevent death or serious injury to a
person - person being you, a family member, or anyone else at all.
The only time you can use deadly force to protect property is to prevent arson.
But be very certain that someone is about to commit arson, and that you can
defend your claim.
However, you can use deadly force to prevent the commission of a felony - so
someone robbing you at gun/knife point and threatening you with injury is probably fair game -- but be really certain that you want to get into a gunfight...
On "on retreat" - it has a history in Oregon.
About 25 years ago, someone was prosecuted for shooting with his concealed
handgun. The prosecution argued that there was no need to shoot, he could have
run away.
The case went to the Oregon Supreme Court. They found for the prosecution, even
though there is no law requiring a duty to retreat.
Now, about three or four years ago, there was a similar case.
The prosecution used the precedent set by the previous case to get a conviction,
and the case found its way to the Oregon Supreme Court.
The court examined the precedent. They were extremely caustic in their comments
about the quality of the legal work behind that finding. They basically demolished
it, and found for the defendant.
So, 30 years ago, no duty to retreat. 25 years ago, you have a duty to retreat,
even though no law says so. As of a very few years ago, you no longer have to
retreat.
That said - if you can walk/run away, I would suggest that as being the best
course of action. You may win in court, but it may cost you days, weeks or
months in jail, and more money than you are likely to earn in the next 20 years.