If you're going to have to head to Newport to get your camping gear you might consider one of the coast streams that have runs of Summer steelhead, like the Siletz which actually enters the ocean just north of Newport. Problem is most of these streams will be very low and clear, the fish will often be stale, and they're not all that easy to hook on the swing. A shot of rain can change all that though, but don't count on rain.
There are lots of rivers that have Summer steelhead in Oregon, but many of them are hatchery fish. If I was coming all that way to hook a steelhead on the swing I'd want it to be a wild fish, so if it was me I'd head for the North Umpqua. The Summer fish arrive there in decent numbers by the beginning of July, and August can be pretty good. Lots of nice camp grounds (I like horseshoe bend)right along the river. The real problem is the heat and sun. Oregon in July and August has pretty much the same weather every day, sunny and warm. We often don't see rain or even clouds from July 4th till late October. With temps in the 90 and even 100's many days, most of the fishing is done early and late with midday hours spent relaxing or sightseeing. In the N Umpqua canyon you can visit waterfalls, hot springs, go swimming, trout fish in lakes or small streams, hike through incredible forests, or drive up to Crater Lake N.P. for the day. Lots of things to do when you're not swinging a fly.
For a real change of scenery the lower Deschutes is a great place to hook a wild steelhead on the swing. It's a desert river, so it's nothing like the east coast, full of sunshine, heat, wind, rattlesnakes, and steelhead. Problem is July and August most of the fish will be in the lower 25 miles of river and you'll have to float, mountain bike, or hike in. The sun is brutal at this time of year, you fish early and late when shade is on the water, then spend the rest of the day looking for shade. It's also extremely crowded, with jet boats and drift boats running the river is big numbers. The competition for prime runs is pretty intense, although it might be nothing like what you experience in the East. I love the lower D, but I stay away in August.
Summer is a great season here in Oregon, I hope you enjoy your trip, and really hope you can hook that steelhead on the swing.
"Perhaps fishing is, for me, only an excuse to be near rivers." - Roderick Haig-Brown