Look into your County's zoning/code ordinances. It should explain in detail what they consider a temporary housing unit or RV in the definitions.
I'm a code enforcement officer for my County and park models are defined as a temporary housing unit here. If the unit is parked at a State approved RV park we don't tax the RV owner, it's done through the park. If the unit is parked at a different site with a Conditional Use Permit(CUP) the are charged a $400 yearly bed fee.
Our assessors office will only tax buildings on a permanent foundation.
You should be able to find your County's zoning/code ordinances online or get them from the planning & zoning department. Being familiar with them will be helpful.
