Cranetop gets away with its dynamic stuff- and i'm going to say cranetop ONLY JUST gets away with its dynamic stuff- by making it the only option. The bomb must be lowered at the start, it must be lifted a the end. At both of these points the bomb fades into the background, almost, and the points become obvious. It is instantly obvious you can't move the cart at these points because it's hovering in midair.
In addition, you can see the cart from the control point and vice versa. There's no confusion about the effect your actions are having. Tieing the control point directly to the carts progression- so it shows on the HUD- helps with this, something that wouldn't happen with a door, say.
To everyone making a lift: use the Capture Zone markings if the size of the cap zone around the cart changes, please.
Players aren't trained to open doors with control points, so will be confused by it, at least the first time.