Did you read the plugin documentation?
Granting the following permissions to a player will cause their owned vehicles to not decay at all.
Vehicle ownership is determined by the OwnerID property of the vehicle, which is usually a player's Steam ID, or 0 for no owner. Various plugins can spawn vehicles with a set owner, or allow the owner to change with certain events, such as Claim Vehicle Ownership. Vehicles spawned by vanilla NPC vendors can have their owner set when purchased via the Vehicle Vendor Options plugin.
If so, then I'll need to update it to be clearer. There is no automatic assignment of ownership as you get in a vehicle or bring it to your base. While ownership of building blocks and deployable entities is set automatically by the vanilla game, ownership of vehicles is only ever set by plugins.
The reason that vehicles decay more slowly inside your base is due to vanilla game logic (also mentioned in the documentation) which applies a 0.1 mutliplier to the decay damage if there is a roof above the vehicle.
Edit: I've updated the plugin documentation to be clearer.