Open carry OK in Oregon without a permit, including in your car, except for 8 cities that ban it:
and a few others I can't think of. If you search around the forum, and also oregonfirearms.org, you can find a pretty complete listing.
Get within 500 or 1000 feet of schools (can't remember for sure which, but it's a federal law, not an Oregon one) w/o permit
Don't go into any public buildings w/o permit
Don't go into any court, even with a permit (there is some theory that certain municipal courts are exempted; not tested)
And obviously, avoid the banned cities w/o permit.
There is an interpretation of statue that your car is private property and not subject to city ordinance banning carry, so as long as you OC in your car, you're OK, even in banned cities. This has not been tested in court, and don't expect much love from our liberal justices for at least the first level of appeals.
As for carrying in your trunk, concealed carry is banned in Oregon without a permit if the firearm is "readily accessable", loaded or otherwise. You're probably Ok even not disassembling it, so long as it's not readily accessable. I know some people that lock them in glove boxes under the theory that they'd have to remove their key from the ignition to get to it. I'm not aware of this being tested, but they haven't had any problems.