As promised, here are some details (and photos) of what I did to "fill-in" the trough left by my removal of the OEM siderails that came on my 2018 Explorer XLT (rather than spending over $500 for all of the overpriced factory pieces):
After removing the hardware, I replaced most of the OEM hex-head bolts with button-head screws (6mm-16), first coating the threads with black silicon sealer and tightening them down securely; then putting some more sealer over the screw-heads, allowing time for the sealer to cure.
As you may know (or find out the hard way), the treatment of where the now-missing plastic "hockey-stick" trim pieces used to meet the windshield can be a tricky area to cover up, due to the bend/shape of the trough in that area. While I at first tried to simply put my flexible, self-adhesive 1" trim down into that area, it just didn't look or fit right, so I had to come up with some other way to do it.
I then researched the two hockey-stick pieces that would have originally come with vehicles that had no such siderail, and ended-up purchasing and installing those (to at least resolve the issue with filling that tricky area). While kind of an expensive resolution, it definitely solved the problem for me.
BTW, the part numbers for those two hockey-stick parts are as follows:
DB5Z-7851729-AA ($51.24)
DB5Z-7851728-AA ($52.18)
After applying new sealer to the bolt holes on each side near the windshield, I reinstalled each of the short original factory trim clips back to their original positions. Once the front portions were clipped back on, I then reused the original hex-head bolts (two on each trim piece) to do the final attachment (adding more sealer to the threads first). I realized that this now left the silver-colored bolt heads showing, even though they were down in their mounting holes, so I glued-in some 11/16" black plastic hole plugs (using even more black sealer), to kind of dress it up a bit.
I then chemically cleaned the rest of the trough, and first put down a layer of 3M automotive-grade rubber double-sided tape (to help smooth-out the bumpy screw areas a little). Next, I applied my Cowles Protekto Trim #33-312-01 automotive-grade rubber adhesive finish trim on top of that.
While certainly not a perfect solution, I feel it met my needs and saved me a bucketload of money, when compared to purchasing the other 8 factory clips and the 2 long finish/trim pieces I would have needed to convert it using OEM parts (and, unfortunately, we don't have any local junkyards where I might have been able to obtain those pieces used)...
