I feel your pain. Sometimes this stuff just does not want to cooperate. Just take a breather, re-plan and refocus. I almost set my pump tunnel on fire a few days ago, I was so irritated.
I don't think I fully understand the problem you are having, but why not bolt it in so that it is at the right angle, then pour some expanding foam in behind them, then sand/shave the foam down and glass over it? The heavier the foam is pretty solid. 8lb will give it quite a bit of support and it is such a small volume, it isn't going to add much weight. Or I could be completely misunderstanding the difficulties you are facing here.
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