OC, loaded or unloaded is lawful in Oregon, with or without a CHL.
However, cities are allowed to restrict loaded firearms but CHL holders are exempt. City of Portland is one of these. They also have a restriction on loaded clips/magazines, while questionable, there has been no one to test it.
Check out the Oregon Gun Rights pamphlet.
Expo center is owned and operated by Metro. OC is allowed on their property and with a permit, buildings. Be careful though, Metro employees could cause an unwanted police encounter due to lack of training. I am pretty sure the Collector West will be checking firearms in at the entrance.
Exciting stuff, I know. What will your table have? I've been needing to buy some target ammo and another box of self defense ammo but I have been lazy. Portland has also been on my list to frequent while OC but I never have any reason to be there unless I am driving through.