Shortly before going full-time, we had GMAC (before the name change to National General) bundle all of our insurance needs (RV, home, cars, umbrella) at what we thought were pretty good rates at the time. This was over twelve years ago, however, and we never had a claim.
Most of the larger carriers will give discounts for bundling. However, we've found that by using a good broker/agent who is aggressive in taking the time to do a lot of research, sometimes savings can be quite a bit by NOT bundling and having separate policies with several different carriers. It just depends on how many carriers the broker has access to. They may find better rates by bundling but sometimes not.
If you're unsure, go out and get some quotes. If you want to save time and effort, use one of the prominent RV insurance brokers (they're insurance agencies but specialize in RV insurance). There are quite a few good ones scattered around the country that can usually write policies in most if not all the states. One that is often mentioned on this forum is Miller in Lake Oswego Oregon ...
go HERE. They will be able to write policies not only for your RV but for your other vehicles, your house, and liability umbrella. It doesn't cost anything to get quotes.
Good Sam is actually considered a broker/agent too but, I believe, have a limited selection of carriers. Their website shows National General, Safeco, Progressive, and Foremost ...and I think they may have a few other lesser-known carriers too but seem to write most RV policies with National General.