Rhubarb is very hardy (zone 4, -20 deg), so you don't need to worry about protecting it from winter freezes even in the coldest parts of Oregon. In fact, it needs a period of cold winter temperatures, below 40 deg, to grow well.
Some basic fall and winter care: don't cut back the stalks until they are killed by a hard frost. This may not happen until late winter in mild areas. The leaves and stems transfer nutrients to the roots as they die, so this is important for the health of the plant.
Make sure drainage is good, so the roots don't rot. If you live in an area where the ground freezes, you can add several inches of mulch over the root zone, but don't pile mulch that would hold water over the crown.
Here is a useful publication on Rhubarb: Grow Your Own Rhubarb.