Had some carpet remnants and made some "floor mats". Nothing pretty but functional. I could find no vendors selling items specifically for the Chevy Express. Will use these until they become too dirty then I will dispose of them and find a better solution.
UPDATE: These were removed and discarded after becoming soaked with water after a heavy rain. The clogged cowl was the cause this and is discussed in the http://roadtrek190.com/viewtopic.php?t=39 Wet Carpet post.