Don't you think we should be able to insure as many cars as we want both online and offline? I think that would make a great mod. The mod could add blips to where one's cars are like the personal vehicles. I know this works with one vehicle online, but why not multiple and offline? 

I want a mod that brings the exact system from MP to SP. The ability to buy garages, personal vehicles and insurance, and of course a mechanic. It would make me play SP more often, as I like to drive my own vehicles that are customized and be able to leave them anywhere on the map and they stay there.

With some luck, I found a mod that imitates the insurance mechanism in multiplayer. Szabo's Persistence Mod allows a character's car to be saved anywhere in the world of Los Santos. No more disappearing cars! More info in the link below.

 

Here is the link: https://www.gta5-mods.com/scripts/szabo-s-persistance-mod

 

There is also another mod that adds the eclipse towers garage, also known as the 10 car garage from online. Instead of having only the ability to store 10 cars, this mod features the ability to store a total of 80 cars since each "floor" consists of a 10 car garage. More info in the link below.

 

Here is the link: https://www.gta5-mods.com/scripts/single-player-garage