Just remember the definition of force. F=ma , where, m is the mass of the system or object and a is its acceleration. For a force to exist, there should be an acceleration of the system (Truck + Trailer + boat). There is no acceleration of the system, the system is moving with constant velocity. So, the force on the system is 0. So, there is no question for the force on the truck to be greater than that on the trailer or vice-versa. Hope this helps you!
Hint: if we apply the third law of mechanics, we can state that at any time the force exerted by the truck on the trailer, and the force exerted by the trailer on the truck are represented with two vectors which the same direction and magnitude, and those vectors are opposed each other
thanks for the medal @bre4h