I would run 17" E rated, I've never had an issue finding 35x12.5x17 for my van. I like the 17 over the 18 because like most here it's fully build out and heavy. I want more side wall and the 17 gives you just that when airing down.
2004 E350 EB Quigley - aka MCSporty6.0
2013 Fiat 500 pop/abarth - Sold
2003 Land Rover Disco II
1997 E350 7.3l 2wd - Sold