I looked at the MidNite website, and maybe I'm missing something, but I didn't see much that would be useful in adding solar to a travel trailer or a van conversion. It looks like MidNite is all about residential solar and I didn't see many pieces that looked like the building blocks of an economical, mobile/portable system. I would say that MidNite and GoPower have about 0% in common in their main target market. I'm not sticking up for GoPower, just pointing out that they are going after a different customer set than MidNite.
I'm not sure it's fair to compare cost per watt between stationary and mobile solutions. I can go down the street and buy residential panels for less that 20 cents per watt, but they don't fit very well on the roof of my RV, they may not be durable travelling down the road at 65 mph, and they aren't really the easiest panels to work with in 12V DC systems. The panels that work best for most mobile applications, charging 12V batteries start at about 80 cents per watt.
If somebody approached me about adding Solar to their RV, I would point them towards something like
this, if they only wanted 200W, but I'd strongly encourage them to step up to something like
this to give them more room for expansion. If they did have room for residential panels,
this kit is probably an even better value in terms of $ per watt.
To get to a package somewhat comparable to the Go Power kit would need an inverter like the Giandel units that Will recommends (about $300), a shunt base battery monitor like the AiLi unit (about $50), a transfer switch, several lengths of various gauges of welding cable/wire, crimp connectors, fuses, breakers and perhaps buss bars. It all adds up, but it could be done for a good bit less than the GoPower kit on amazon.