Marshall has been there, and been doing that for decades. His output, especially for the hugely long routes, is prodigious (think running across the US).  

"What I was doing was kicking back and having fun.  Showing people you can do more".

"Kicking back and having fun"?  Running across Death Valley a total of 29 times doesn't strike me as that much fun.  But that's Marshall - taking humble understatement to a whole new level!  Marshall exemplifies a theory of mine: "Hardcore people never think they are. They think what they do is normal, because hardcore is all they know. People who think they are hardcore rarely are."

"My friend and I did 8 Eco-Challenges together. We thought of it as fun - we didn't think it was anything extraordinary."

Yeah, right!  Marshall also did Badwater (lowest point to highest point in the US) Unsupported Solo!  He brought all his own water for the 146 mile crossing during July.  How did he do that??  You're about to find out.