He won't "thicken up" like a bichir does, so be careful not to overfeed him. They're called ropefish because they're rope-shaped, after all. He does look a little skinny, but not abnormally so.
And yes, cover EVERY hole. I would not keep a ropefish in any kind of a tank with an open (hang on back, etc) filter, and you have to be careful about them getting into overflows that don't have large enough openings as well.
One of the first fish I got was a ropefish, and they're still amongst my favorites, but my first guy escaped by swimming up the waterfall of an AC70 and knocking plastic I'd put there out of the way. Came home to find him dry on my living room floor, and my cats surprisingly terrified.