There is no need to have the /fix to repair your trailer. If someone has intentionally caused significant damage to your trailer, you can use an autosave to 'roll back' prior to the incident.
As far as I'm concerned the /fix should only be used to negate 'trollish' behaviour and not to give you infinite free repairs.
F7 represents being towed to the nearest garage (at a cost) so that necessary repairs to your vehicle can be carried out & paid for.
Normal repairs should always be paid for.
Damage over the normal wear & tear can be averted by changing or improving a persons driving style.