trailer drip tray
Most tractor drawn aerials will have a small compartment under the ladder compartment on the back of the trailer. These compartments have a hinge on the bottom and open from the top.
Because this compartment opens from the top, water can find its way into the compartment. (Click to enlarge)
An easy solution to solve this problem is to install a small drip tray above the compartment. (Click to enlarge)