Thule roof track parts?

[Twindaddy]

Resurrecting this for some help.
I actually located the details of the van I purchased used. As it turns out, the prior owner had Yakima rails installed. No big deal - they're all about the same, right?
So I ordered a nice set of Rhino Racks at a good price with multiple fit kits. I thought that was a great bonus. Those racks arrived last weekend and look top notch.
Today I went to install them. Should be simple, right? Remove the end cap at the rear, slide the square nuts into the rails, position, tighten, etc. Sadly, the first step was a failure. The screws holding the endcap in place just spin. Not freely - they're clearly well sealed in there, but they don't grab anything enough to back out. Then I notice that the rails all have round headed screws in them instead of recessed. So even if I can get these caps off, I can't slide the nuts past the next screw. I'm not inclined to remove these and introduce the possibility of leaks.
Is this unique to my van? Did the installed mess up both the rails, in terms of the screws, and the workmanship in that the endcap is screwed into nothing?
Anyone else have to struggle through what should have been a simple rack install? What are some creative options I may not have considered?
Thanks in advance!

[Scalf77]

All my screws were outside of the penthouse canvas, so any leak in theory would be outside. I replaced the small washers that were used in the original installation with larger fender washers and used butyl rubber instead of the silicon sealant that was used. The round head screws also used, but if tightened down good, the square nuts usually went by, maybe some with persuasion.



-greg

[Twindaddy]

A picture can say 1000 words, right? For me those words started with "what an idiot I've been..."
I had pictured, in my head, the screws going into wood or something "sandwiched" in the roof. It never dawned on me that those button covers in the ceiling were to cover the nuts from the rails.
I popped off the two end covers, got them in a vice grip and was able to loosen them from the top. From there I was able to remove the end caps (a bit brittle from all the years in the sun - I may replace those) and get the rack feet and crossbars mounted. Indeed, with a little tightening of the roof rail screws and some persuasion, the square nuts made it past.
I replaced the end screws with some fresh sealant and all is done.
I did notice that it'll soon be time to re-seal the larger bolt/washers on the roof, but that's for another weekend.
Thanks for the assist, the suggestions and the picture. They really helped.