I have a long-haired dog who sheds a lot - she also likes to run through the
mud.  Since I prefer carpet in my Westy - for comfort in winter and for
sound-deadening properties, I take a regular bed sheet and fold it to fit
the carpet area in the middle of the van.  I hold the corners down with
various odds and ends - water bottle, heater, etc.  When I get home from an
outing, the sheet is usually covered with mud and doghair.  Shake it out -
throw it in the washer - and voila, clean van, clean sheet for next trip.

Maggie
'85 Subaru-Westy "Anne Bonney"