Check out local 'County Fairgrounds' in the direction of evacuation. Almost every town has a fairground. Many RV'ers are not aware of this being available to RV's so they don't fill up as fast as CG's during a storm.
Once I found out about fairgrounds having CG sites, I actually made them as part of my CG stays while full time RV'ing. Very reasonable rates, hookups and spacious sites. And there is always a minimum of one dump station on the grounds sometimes more.
During hurricanes They always open up all fairgrounds as shelter for RV's. Also for those with livestock because of all the stalls at a fairground AND it is always open for a destination shelter for pets.