You are right. That is a very touchy connection. Its also one that manufacturers of composite aircraft have been dealing with for years. You could Google "composite bolt connection" and similar phrases and you will get several hits, some magazine articles, academic papers, etc. There are many approaches, but two common themes in all of them. (1) Spread out the concentrated load over as large an area as possible. (2) Consider the strengths and weaknesses of composite materials from the beginning. (Strong in tension, not so much in compression and shear.) They don't just design a tub and then figure out how to attach a seat. The loading from the seats is considered from the very beginning. The actual bolted connection is one thing, but the configuration of the composite shape around it is equally important to properly absorb and distribute the loads.