Last years IRV2 rally was held at River Plantation. If you want to be based in Sevierville, this would be as good as any.
If your main goal is to tour the park, I'd probably head for Gatlinburg so as to avoid the horrendous traffic between Sevierville and the park entrance. It's been a few years, but we enjoyed our stay at
Twin Creek.
I know there are others, just not that we've had personal experience with.