I'll take a crack at answering your questions; if I am wrong, I am sure some one will correct me.....
A) Oregon is a open carry state (for the most part anyways). Carring a side arm on your hip, in a holster, and plainly visable shouldpose no issues.
B) Aside from the federalrestrictions, schools, fed buildings, court houses ect, you should be able to open carry in most all public places, except in the "banned cities". The ban in essense restricts "loaded hand guns"
B1) Loaded meaning " any rounds in the weapon" period.
C) You should be able to openly carry on private property unless posted. If you are asked to leave for what ever reason; you should simply comply and avoid any issues.
D) In your vehicle (private property) you can carry loaded, but not concealed. Law enforcement should be able to have a "clear line of sight" from first contact. However, if your traveling in a RV and are100+miles from your residence; it becomes your "residence". In which case you can "store" a hand gun concealed. Law enforcement can'tspecificlly "see it" straight way because it's "in" your mobile "residence".
Outside of the greater Portland area, Oregon in general is quite accepting of open carry, I have never had an issue and carry open as often as I can.