Yes we have to leave the key in ours when its not attached - a pain but ours is protected by a cradboard sleeve.
We tow with the 'new style' CR-V and it handles a Bailey S6 Bretange great. We have a Honda removable towbar fitted too.
As far as removing the key from the tow ball. . .Look at the rear part of the ball, the part that connects to the car. There is a little steel button that gets depressed by the action of replacing the towball back into the car section. Use something to press this button keeping your hands away from the plastic locking turn as this spins a quarter turn.
Before refitting the towball to the car, you need to turn the locking turn, basically repeating the process of removing the towball from the car in the first place.
There are alot of words above, but when you have done it a couple of times, it becomes second nature!! And it also removes the possibility of snapping the key while its retained in the bar. . .
Good luck with your mission, should you accept it.
This message will self destruct in 1 secon. . .BANG!!!!!