Take a tape measure and measure the area, it's rectangular and nothing
tricky.  Now go to your local el-cheapo local carpet merchant, the guy
that runs the obnoxious adds during the late show.  They will have all
kinds of remnents.  Have them cut you a piece, with one long edge from
the finished edge of the carpet roll, probably from commercial or
indor/outdoor carpeting.  Chose a color you will like in your Westy.
Take it out and drop it in with the finished edge at the door.  Your
done, and it should cost you from seven to fifteen dollars max.  I've
done this three times, great solution.  If you do a lot of camping and
are tired of sweeping out the leaves, twigs, dirt etc., get two or three
like this.  Stack them up on the floor for travel or everyday use
(additional insulation and sound deading) and when you set up camp, pull
out the extras and put them on the ground in front of the door or use
them however they will help around camp. If you like, you can store the
outdoor use carpets under the 'good' one all year round for appearance.
One word of warning: if you live in a very damp climate, make sure you
don't 'stack and store' these inside you Westy if they are damp.  Rapid
mildew problems and the orders are near impossible to get rid of.