If the towbar is locked also allow use of the trailer brakes. When the brakes key 'B' is hit also activate the trailer brakes. The parking brake toggle should also be respected.

Based on the trailer towing tests I did a couple weeks ago, I'd consider this something that should be an automatic feature of locking the towbar, but it would be acceptable to have a PAW toggle switch to enable/disable braking assist similar to steering assist.

Rationale is that trailer brakes are common. Legally all USA states require trailer brakes at some point and only differ on the minimum weight of the trailer before they are are required.