I would expect you to get 300 Wh on average from charging all day while traveling. I decided against it even though I could extend my range some with it. It's a pain in the ass, hinders getting anything out of the trailer, is fragile and I will stop anyway for breaks so I can charge. I have an 800 watt charger so I can charge about a mile a minute.I'm using off the shelf components for ease of assembly, cost, and time reasons. Like I said in the first post, I wanted a higher wattage panel, but not the larger size. Just like the guy with the custom build said, it's all about trade offs.
I would have bought the trailer anyway, even if I didn't add a solar panel. The solar panel is somewhat of an experiment, and appeals to the techie part of me.