Tofino/Uclulet is pretty amazing. Long Beach is world famous and attracts visitors from all over the world. If you don't go there, if you have the $$, visit Tofino in the winter and stay at
Wickaninnish Inn and watch the storms and waves from your room next to the beach. Stop at
Macmillan Park/Cathedral Grove on the way to Port Alberni and see humongous trees that are up to 800 years old.
Another option to Tofino/Uclulet might be heading southward out of Port Alberni along Barkely Sound towards Bamfield and
Pacific Rim National Park. I have no idea about RV campgrounds around there. If you have the time, consider a one-day cruise on a
Lady Rose Marine ship through the Sound.
Campbell River is also a good choice and because it's on the eastern side of the Island is protected from the ocean breezes and will generally be warmer. From Campbell River on the way back, an option is to drive down to Comox and take the ferry over to Powell River and make your way down the Sunshine Coast to West Vancouver. The Sunshine Coast is very beautiful and worth the effort.
Strathcona Provincial Park is west and south of Campbell River and has great day hikes. There are boat rentals at Buttle Lake on the way to the park. There is also
Elk Falls Provincial Park which is closer to Campbell River. There are many fishing charters available in Campbell River
(such as this one). They call CR the Salmon capital of the world.
Alert Bay was mentioned above. It also would be a totally amazing trip. Would be quieter and less crowded too.
Doesn't matter where you go on the Island, it's all awesome!