Columbia River Gorge Washington State Campground?

Maryhill Park on the WA side. Fire up google maps and you can see them for yourself.

I agree with Maryhill. Whether you take 14 or I-84 is a draw, IMHO. If you've never taken 84, you may not know that it is very scenic, for a freeway, is in excellent condition and the traffic is light once you get out of Portland.

You will miss a lot if you stay on one side. I would suggest camping on the OR side in most places and then day-tripping to the Washington side.
If you are comfortable on twisty roads WA 14 is for you!
I-84 east out of Portland.
Just east is Rooster Rock and Multnomah Falls. There is stretches of the Old US 30 going both directions. Would be difficult going with the rig.
Across the Columbia you will see Cape Horn. WA 14 is very narrow around the cape. Farther east on WA side is Beacon Rock.
Great stops on either side at some the dams. There is campgrounds near each of the dams.
Near Plymouth, WA Umatilla, Or area is a great Corp park. Many wind surfers visit this area.

Sandy Riverfront RV Resort Troutdale,OR is a decent full hookup park. Troutdale is at the mouth of the gorge. A short drive to all of the water falls on the Oregon side. I would suggest you plan to drive up the Oregon side on old hwy30 as far as you can go. Drop onto I84 for the short drive to Hood River, cross the bridge and back on Hwy14 in WA. Crossing back on the I205 bridge to I84 and Troutdale. That is a nice one day loop. But if you don't mind hiking a bit you could spend a couple days hiking the trails in the gorge around the water falls. Be aware, May is still wet season here, so be prepared for rain. Also stop at Bonneville Dan and the fish ladder. There is also a fish hatchery near by that might be worth a visit.

Maryhill is a very nice park, we stayed there last year for 3 days. Stonehenge and the Maryhill winery are really nice. I took 84 west from there to Portland, very scenic, nice road.

As mentioned, Maryhill is nice. The museum there is neat to see also.
If you want to go a bit farther east, Crow Butte is nice too. It's on an island with some hiking trails, some wineries nearby, and a major destination for water sports.
Columbia Hills State park across the river from The Dalles is small but pretty nice also.
On the Oregon side: Ainsworth, Memaloose, and Deschutes River State Rec Area are ones we like.
Fair warning: almost any of these will have trains running adjacent to it (Crow Butte they're across the bay, maybe 1/2 mile away) and the Oregon side ones will all be near the freeway.

What's your height?
I'd have to get the Truckers Atlas out of the truck, but there is a warning on two tunnels on WA-14 between Vancouver and Mary Hill SP

I'd stay on I-84 and pick one of the Oregon SP's for a place to stay. WA 14 is narrow and twisty, not good for RV travel in my mind and I've been on both highways many times. As somebody suggested, camp on I-84 and take day trips to the old Columbia River Highway (on the OR side), Pendelton Woolen Mills in WA just east of Vancouver, Maryhill Museum, downtown Hood River, Multnomah Falls, and all the places to visit.

May is when the reservation system starts for most WA SP, so you should check out the dates you think you'll be there and see if anything is open. Weekends fill up fast, but during the week, you can get lucky..

We can reserve up to 9 mos ahead and all the best sites go fast! Maryhill is a popular SP, so if you want hookups, you have to reserve.. You might get lucky and get a standard site by just pulling in, but every time I've gone there, it was "CAMP FULL" signs upon entering.... ;) I take I84 on the Oregon side to get there and just hop the river to get to Maryhill..

If you like Astronomy, the Goldendale Observatory is pretty cool and the other sites mentioned will keep you busy for sure!

It can and does get windy there, so be prepared for that..

Mitch

Organized campgrounds with hookups etc. or dispersed camping/boondocking?