That’s what I would do, is use the official STP bus.
When you arrive in Portland – I am assuming you’re doing the 2 day – here’s the drill.
Walk your bike immediately to the truck and load it. With luck, your bike will arrive back in Seattle before you do. You don’t need it any more, anyway.
Walk to your luggage in the luggage room. Put away things you don’t need immediately. I think your $250 pair of sunglasses are safer stowed in your luggage than left outside while you’re taking your shower. Just get the stuff you need for your shower out of your luggage; leave the rest there.
Get in line for the shower truck. You’re male, you have to wait. We ladies usually get to just waltz in. Take a shower and change into clean clothes. You’re now nearly human.
Walk to the food stands. Get yourself a burrito, gyro, or some other substantive snack. Walk it into the beer garden, and drink a beer while consuming said food item. Your humanity is now completely restored. The beer garden then also gives you a place to rendezvous with anyone who you might want to rendezvous with. Regale others with stories of the last two days.
Now that your beer has rendered you sufficiently mellow and you’ve had some restorative calories/vitamins/protein/carbs, you’re readyfor the bus. Walk back to your luggage, and stow all your things away. Check out of the luggage room with all your stuff and board the bus.
Board the bus, snooze, look at all the miles roll by out the window that you’ve rode over the two days. When you get off the bus, with luck, your bike has already arrived, and you can fetch it and put it on your car, and drive away.