I am running a subpanel off of a 30 amp breaker, I need to run a smaller subpanel off of that. Can I use a 70 amp rated panel for my 30 amp service feed, so that I will have room in the panel to put in a 20 amp double pole breaker?
Yes you can. It is quite typical to have a sub-panel (non-service panel) rated higher than the feeder that feeds it. The rating of the panel is just the maximum it can be fed with.