+1 on Canyon RV. The only thing, I'm not sure about net access. It isn't listed and the sites are spread out pretty wide. You'd have to call and ask about that. It's a nice quiet place. Never camped there, since it is in my backyard, but go to the truck show there sometimes. Weather will be great in November.
I agree what others are saying, using East Shore or Canyon RV Park.
But if the problem is with the length of stay at both Pomona KOA and East Shore due to the size of your rig, how about staying at the KOA for 3 weeks then moving to the East Shore. They are very close to each other. Sounds like these two are the most centralized for the area you need to commute to.
I like Canyon RV Park too, but as others have said, depending on the time of day you commute, that 91 freeway can be a bear. But it is a nice, rustic park with lots of space. You do hear the freeway noise constantly though.
Good luck, hope you enjoy your stay.
California has really strict rules about long term rentals, even at campgrounds and RV resorts. At a certain point you become a tenant and are subject to all the rights of a tenant. Once you become a tenant it is very hard for a campground to make you leave. They have to go to court and get an eviction order to force you to leave. I'm almost certain that is why the campground has a three week limit.
There is a huge problem in California with homeless buying old RVs to live in. Many California cities only allow an RV to park on a public street for a limited time to stop the homeless with their run down RVs from just living on the streets. Again, I would guess that the issue with old run down RVs is the reason why California campgrounds are so strict about age.
California laws are often ridiculous, but the last time I ran up against this the legal line was crossed after six months in an RV park.
Golden Shore in Long Beach has monthly rates, so they won't throw you out after 3 weeks
One strategy regarding traffic is trying to be located so you are going against the grain (outward in the morning and inward in the evening).
You might also try Orangeland http://www.orangeland.com/
Its near to the 5 and 57 freeways, as well as Angel Stadium and Honda Center/Anaheim Pond
Their site says free WiFi.
Honestly, given the list of places you want to get to and from there's no one good place to be. If you're out near Pomona then Irvine and Lake Forest will be at least an hour drive even on the weekends, and potentially much more.
I would definitely suggest Anaheim/Orange as a more centrally located solution San Bernardino and West Covina are probably 90 minutes with decent traffic, LA, Riverside and the others probably closer to 60 minutes.
If you need a quick overnighter, there is also a Camping World off the 5 @ Valley View that allows overnighting in the parking lot, but no WiFi or other services.