Galloping Goose was quite nice, we did it in the opposite direction. The road from Renfrew to Sooke was a bit average with the traffic and being narrow. The Campground in Port Renfrew was notable for having the worst facilities to cost ratio we encountered between Vancouver Island and San Francisco. $25 for a patch of sand and a drop toilet, and somebody else camped on our patch of sand, leaving us with an even less attractive bit of sand. Plus there was the 2km ride to the campground office tap to get drinking water. We did a logging road from Cowichan to Renfrew, past the Avatar Grove. The road was steep and rough, but scenic. The log trucks were the best vehicles we encountered. When we heard them coming we got off the road. They must have passed the word around, because we noticed the would slow down before they got to us (even before they could see us - probably talking on the CB) and just cruise past at 15-20mph, give us a wave, the speed up.
Not sure about the Cowichan Trail, we rode down from Bamfield.