'59 fiberglass endcaps

[1959newbie]

I am SO excited to be at this point, but I need some help from those of you who have removed and replaced fiberglass endcaps, please. They were the last thing out, so they're the first thing in.

But I'm having fits getting rear fiberglass re-aligned with rivet holes! Got several rivets in around windows and one or two on arched rib at forward edge of end cap. But can't seem to wrestle the @#$% thing into place. And it is so flexible AND brittle, I'm nervous about over-stressing it. There's not really any way to use clamps on this piece, either -- nothing to clamp to!

Also, does window trim aluminum get riveted in simultaneously with wall panels, or after? Seemed on dismantling that they were separately riveted, but around this rear window, it's looking like maybe I need to use single rivets thru everything: frame, fiberglass & window trim.

Thanks for any help,