I am a Washington resident working in Oregon. I will transport my firearm( pistol) with me to my hotel. I know it's allowable to open carry in Oregon, but how do I do that legally in my vehicle?  Thanks

Take a look at Oregon law 166.250.  If you read the law for yourself, you aren't relying on someone mis-interpreting the law for you.  You can even print the law and keep it in your vehicle along with the handgun.  

I don't think it is in my best interest to rely on random people on the internet to interpret the laws for me.  I like to read the law, and read any relevant court decisions for myself.

As a former Oregonian, without a carry permit you need to keep the gun and ammunition stored separately and the gun inaccessible while driving.

As for open carry, it is state law to allow it, however local municipalities have their own rules around it. If you’re traveling to the Portland metro area, be sure to check local laws for each town you’ll be traveling through. Oregon is no longer a gun friendly state.

Disclaimer: I am NOT a lawyer.

Outside of certain cities (Portland, Salem, Eugene) as long as it's not concealed it's fine. In those cities keep it secured in a locking container (locked glovebox works), or unloaded. If you regularly travel to Oregon it would be worthwhile to get your CHL. Multnomah County is probably one of the easier counties for out of state residents. I would recommend a lock box anchored to your vehicle for security.

Have heard Long beach and Longview to Columbia and Clatsop Co. are easier to obtain.