Last I read Washington State was very similar to California. It's OK as long as two way communication is established.
I would keep them away from the upper bed forward window if equipped. Maybe cover the forward window with plexiglass. If equipped, the upper bed forward window is probably plate glass.
Depending on venting, keep all TC windows closed while moving. It's possible to suck in toilet fumes/smell if a window is opened while on the interstate.
FRS radios should be good for communication if legal where you live. I have carried the dogs back there on a very short distance. I also used a remote wireless temp monitor to watch the temp.