[@KiwiTime] I love that little concept. You can go in so many directions with it and the moment if / when they finally get their hands on some power armor could be a great payoff. 

Regarding what I've done with the system using D&D, I have a full PDF write up that I'll share privately with everyone once we move forward. Yes it uses the foundation of D&D 5e (d20, advantage/disadvantage, leveling up, etc.) but honestly it stands on its own in more ways than it's similar. I've replaced the class system with a "build your own character by selecting perks" system that is more akin to using Feats in D&D and things like that. The guts are there because they are a solid foundation...but I've put a lot of effort into making it feel like Fallout and make sense. Once I stopped overthinking it things became so obvious and smooth and just fell into place. 

The rules are lighter than 5e, easier to remember, and fit nicely in the background of the most important thing...which is the stories we tell :D.