Dave, your procedure exactly as described will 'work', without requiring any new permanent wiring. Indeed, it is exactly what many folks with generators do. BUT, it does not have a safety interlock, and puts linemen at risk. If someone flipped the breaker back while you were running (ignoring your tag) your genset would backfeed the grid. Instead, get an interlock panel, and it will mechanically force one (new) 240V 30A breaker to be 'off' whenever the main breaker is on...that 30A line can go to a (new) locking outlet, located wherever you like, that will be dead whenever you are on grid power. Use that with the same cabel you made up for your idea, and you are 'safe'. I was saying (confusingly) that if you moved your dryer to that new breaker, it could never connect to grid power...it would be locked out.