Just so I'm clear, you said "hello to Portland" yet you are thinking of moving to Corvallis or Eugene. Is that correct?
As I'm sure you know Corvallis is about an hour and a half and Eugene close to 2 hours south of Portland. So recommendations of places in Portland may not be helpful.
I think if you're going to be in the corvallis/Eugene area, it's got a fair amount of Open country around it. so I don't think you'll have much of a problem finding a place that you could store that size of bus where you choose to buy / rent.
Best of luck.