Welcome commdiver, to the best DIY'r site on the web.
If you did make up a 30 amp extension cord, where would you connect it?
You would still need a 30 amp plug (male and female) or are you asking to just wire directly to a breaker on a sub panel.
Either way will work, as long as the circuit, wire and breaker are all rated appropriately.
When its all said and done there is usually more said than done
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