Woodland is southern WA near I5. lake pleasant rv park is closest to I405, though not too far from the north junction of I5 and 405.
405, though a belt way is till busy during rush hours, since it passes through Bellevue - an employment center in its own right.
WSDOT and Google Maps have travel statistics by day of week and time of day.
You might want to bypass the core of Tacoma with the freeways through Puyallup (167 and something else).
Events downtown Seattle affect evening and weekend traffic, less so on 405. But check the travel alerts on the WSDOT website. Lots of good travel information on the WSDOT site.
WSDOT Seattle traffic map archive