This is the only RV campground I could find on the north side of Big Bend NP and I would stay here again.  And as I'm used to staying in many campgrounds located near highways and significant city traffic, Stillwell is completely opposite -- totally quiet & dark & pleasant!  On our drive to the park one day, we saw a sizable family of javelinas crossing the road!

The website is very clear that there is no cellular and very limited wifi (basically just at the store, although my wife's phone seemed a lot for successful at finding and holding the network from our place at the far end of the full-hookups lot.  There are zero trees and I saw a couple Starlink receivers so I presume they've got full connectivity!

The FHU sites are very narrow.  Each post has connections for two sites, so you and your neighbor pull in from opposite directions (assuming you both need driver-side hookups.)  This is shown clearly on the site map, so no surprise there.  But, we have a 42" deep slide and, even with just 6-8" clearance from the post, the adjacent site (on the curb side) with a similar slide would likely result in a single narrow shared path between the two rigs.  Said another way, if I had to guess, I say there's only about 32' between posts to fit two rigs.

Our site, at least where we stopped in the long space, was significantly unlevel, both side-to-side and front-to-back, although we tried a few stopping points.  The sewer connections are raised high above the surface, resulting in limited actual draining of your tanks even when using the common tapered hose guides we all use (i.e. significant waste will remain in the line.)  Plan some extra time and care to dump and rinse your line.   

As I said, I would definitely come here again, but just be prepared for this campground's less-than-ideal quirks.  And enjoy the peace & quiet!