You should be able to attach camo nets to parked vehicles.

The military does it in real life so its not unpractical and it would help in game to hide vehicles a little better.

Have had multiple cars on official go missing due to someone finding them due to the bright colors or they just blow them up on me.

You could add the ability while in the cars vicinity select screen to have a camo net slot and or have the camo nets in hand and press RT (right trigger) to attach it to the vehicle.