I bought the biggest ugliest cheapest plainest mudflaps I could fined, 1/4"
rubber slabs 20x12 size. $7.99/pair.  Turned them sideways and mounted then
with stainlees steel machine screws and washers by drilling holes into the
jack post beam, just below the body floor.  They reach from the inner side
of the wheel well across to 1/2" outside fender lips. I drilled one hole in
the fender lip inside the wheel well(not through exposed paint surface) to
hold that corner in place.  Huge 20" wide mudflaps that hang down about 8"
below frame.  As big as feasible.

Do they work?  Well as air brakes maybe :)  Still get snow running boards
built up fast in winter, starting at the 2nd floor brace instead of full
length.  Crap still all over the sides of the bus too. Propane tank encased
in frozen slush....   really don't think it was worth it.  On a loaf I'd
used the same flaps hanging down almost to the ground. This worked great,
until backing up in snow pushed the flaps into the tires whence they were
both torn off instantly.  Now I know why some transport trucks have 'chained
down' mudflaps!!  I'm advocating full wheel well covers for all, enclose the
entire tire, fronts and rears, go for the 50's car of the future look!!
YMMV, tim

ps: to protect from rock rash underside apply the rubberized undercoating
spray every second year.  this will cut down on rusting.