Repair trailer usable without attaching

The idea is that repair trailers should be usable without attaching it to a truck, just like fuel trailers.

For example, you find a repair trailer, the big green one with a scout and you cannot use it until a truck comes and attaches it.

Mechanically, it could work like the refuel option, and it would be nice if we could also move repair points between addons. For example, a big repair trailer could refill a small scout addon of repair points.