So I've been using KAC rail covers for 10 years now.  Since from the beginning, the rails were never rock solidly mounted.  They have a little play where I can move the panels back and forth with some force.  I never noticed it while shooting but still know that the panels can shift.  I used 550 cord to help take up some of the slack but still is not a tight fit.  I was using KAC covers because Larue handguards have this integral QD socket as shown in picture number 1.  KAC rail covers enabled me to cover over the QD socket as shown in picture number 2.  I am looking for replacement covers that can cover the QD socket of the Larue handguard but have a tight solid fit.  The KAC were too loose.  Also the rail panels must be able to cut down for a custom fit on my hand guard.

for full quad rail low pro light ladder rail covers are the way. I have a stealth myself, its a heavy bitch.

LaRue Index Clips for the win! They are by far the very best rail covers I have ever used and I've used quite a few. They are also the very best for wire management too.

Tango Down...I've replaced all KAC panels w/them.

Op, firstly its time to start using those qd mounts instead of covering over them. Secondly, there is only one other product that will do what your looking for and that is the gen 1 magpul Xtr rail covers (gen 2 will not work). The reason is, you are trying to put a cover over an area that does not have ladder cuts, but still has the "dovetail" edge. You need a cover that mostly grabs on the outer edges of those dovetails instead of the ladders.

If your not open to using qd sling mounts, then either don't cover them, or use gen 1 magpul.

Manta rail covers are capable of doing what you desire. They only have small lugs on the under side every so often, not every slot. They cut easily to any length. You can seamlessly add them together, or cut the picitinny engagement lugs out of the bottom if they interfere. They have small metal bands molded into the rubber material that you pinch to the rail for a secure hold, so you really only need one lug to keep a section of cover from lateral movement. I ran them on my LMT MRP and was able to cover the front QD mount I did not use. Still have some in the parts bin. Skip to 2:10 in the video below to see underside of the covers and how they mount up.

Manta Rail Covers Video
My old MRP with Manta covers over front QD
Attached File