He should ask if the topper is worth it when he is having to get back into town, has to get a ladder out when it is raining to pry out a pine cone wedged on the top when trying to bring the slide in.
I'd take the slide topper any day. It might add a little bit more stress, but the potential water damage it protects against will cost a LOT more to deal with than a fixing a slide motor.
As a compromise, I'd ask him about a Solera slide boot/slide sleeve. It does not use a spring, nor has spring tension, and does the same job as a slide awning. The complete boot even protects the bottom, making a very good barrier against water intrusion.