Brown's Camp in the Tillamook State Forest is the OHV area closest to Portland and has a great variety of trails. I would recommend starting there once the stay-home order is lifted.
Also, Jones Creek outside of Vancouver (WA) supposedly has some Jeep trails now.
Installed the M.O.R.E. dead pedal on Saturday. It wasn't too bad, thanks to this thread. Thanks to everyone for posting their experiences!
(I used a small vise grip and some painter's tape to keep the pieces in place during the install.)