Why they chose the RV place has always been one of my biggest questions.
I don't even know if you can see the RV place while driving on I94 at interstate speed, especially since there's a Sams club between it and i94 now.
It seems more likely to me that they would have noticed it while going down Main Ave in Moorhead to get onto I94, either on that night or a lot of previous trips.
They would be going slower, there are signs that say industrial Park entrance etc. But, I don't know how many people use that route as their preferred way to get on I94. It would depend a lot on where they're coming from and where they're going.
The RV sight would be a perfect place to go if you needed a place to meet people on a neutral ground if you were going to perhaps exchange something illegal. Off the beaten path, some lighting, easy in and out access, obstructed view due to the RV's, chances of getting interrupted are slim. Big problem is, it would be a great place for an ambush. Maybe it seemed like a great place to leave someone because you could offload quick without having to drag down to a river, or throw over a railing because you didn't have time to drive all the way out to the woods, or to the middle of a field, especially if you are not familiar with the outskirts of town.