Well, for Blastmaster in particular, I believe I mentioned at one point that he was created in the moment between when they opened the door out of Peaceful Acres and when they walked through it. But what I eventually ended up figuring was he was a mercenary that stumbled onto one of the abandoned national guard armories full of explosives (and at least one bomb squad suit), and devoted a year or so to using the demolitionist training manuals there to use them safely, eventually moving on to missile ordnance guides and pyrotechnics training books from a Florida fireworks factory. Some corporation had to keep Kismet Park alight at night, after all. And eventually, in his self imposed exile, his mercenary corps moved on and left him to become his own force.