The rain gutters are designed to be attached to a house with brackets that keep the tops opened. Without the brackets the tops of the rain gutters bow inward quite a bit. unfortunately, I didn't realize this until after the end caps were glued on.
Ahhh well. Here is how I installed the brackets on the two troughs that needed them. I did buy 4 brackets just in case the other two felt inclined to bow inwards in the future.
1. These are the brackets I bought after the fact.
2. Mark the middles of the troughs that need the brackets
3. Angle the bracket up under the outer lip and lever it in place.
4. Outside of bracket in place
5. Long view of outside of bracket in place.
6. Get your trusty assistant to assist you while you pull the inside edge of the rain gutter up and have your assistant force the bracket down over the lifted lip of the gutter.
7. Use a flat blade screw driver to force the inside edge of the bracket up against the lip of the rain gutter.
8. Use a flat blade screw driver to curl the upper lip of the rain gutter in place over the edge of the bracket.
9. Viola! the bracket is installed!
Repeat as necessary and then go nurse your torn up thumbs from trying to deform the silly lip of the rain gutter.