The end caps are structural, although somewhat minimally. Back in the dim and distant past they were made up of segmented aluminum. This can be done, of course, but would be tedious. For a few years they were made of fiberglass, then came the abs plastic.
Here is a thread on how I repaired mine:
http://www.airforums.com/forum...hlight=end+cap
There is a photo as well. Not a great one, but it is hard to get them to show up well in a photo.
In reviewing that post I see I failed to note one significant portion of my repairs: I used scrap pieces of abs to reinforce the back side of the cracked areas before patching and painting. I simply solvent welded them with abs plumbing cement.
I also had a bad crack in one of the corners of the bins. Again, I patched it from behind before painting, then reinstalled the bins VERY carefrully.
Mark