Jack,
Your 2008 E-350 should be pretty well set for the stuff they sell as motor fuel. unless you work pretty hard, you will find it tough to find something other than crapahol at a fuel pump. There is a website called
Pure-Gas that will lead to real gasoline, but in the lower 48 it is not always easy to find. I did a lot of boat work before the depression killed our business, and by the end in 2010, the alcohol problems were fixed in the older baots. There are so few newer boats here, I just have to guess that this is a dead issue.
People ask how I know so much about RVs. (They may not know that I have actually had one for years.) I tell them that they are just boats that don't float very well.
Do you know the one really big difference between boats and RVs??
Water can leak OUT of an RV.
Matt