Yup, "rivet nuts" work well, but CAN be over-tightened. Also, your piece of ali angle sounds a bit thin, AND the rivnut tool and the nuts aren't cheap.
For a one-off job I completely disagree with a previous poster who says that epoxy will not be reliable. It will be VERY reliable in my experience provided that you definitely do/use:
1. The original (24 hour) Araldite, or, more expensive, the West epoxy system, and;
2. Not only abrade the area AND the nut before adding the adhesive, but also, MOST important, make sure that all surfaces to be contacted are 100% clean (e.g. acetone) and after that NO fingers on the area, and;
3. Especially if using the 24 hour Araldite make sure that the job cannot possibly move even a little bit throughout the 24 hour cure time - i.e. some sort of "jig", made up before hand (bit's of soft wire, tape, wood, whatever you can make work).
A couple of "good idea" additions to this particular job:
4. A scrap of sheet ali cut to shape to thicken the web you're going to be bolted to. Can be held "temporarily" in place with one or two self-tappers, but will be held firmly by the epoxy once cured, and;
5. The idea of a Tee slot to provide an additional mechanical lock is also good. It depends how much space you've got to work with/how thin the material is.
I've had lots of experience of such work, both in my shop and with "official" repairs to aircraft (where you follow the instructions EXACTLY). From my experience, every time you hear of epoxy joints failing it's because they weren't scrupulously clean before/during application, and/or they moved during cure time.
For the "right job", a good quality epoxy is the best repair you can get and only fails due to poor application such as lack of cleanliness. The only epoxies I've ever used are West, Araldite 24 hour, and Devcon 5 minute. I'm sure there are other good ones but I don't know them.
HTH
