Sure is.

Exhaust gases produce droplets of condensation that build up in the muffler.
Under normal driving this condensation evaporates when the muffler gets hot
from use.  Driving the vehicle is enough to get rid of this water vapor.
However only driving it for short trips or to the shops does not give the
muffler a chance to heat up and evaporate this water hence the rusting.

Stainless Steel may be your answer but personally I would plan your driving
trips a bit more.   Its a safe bet to say if your muffler doesn't reach optimum
operating temperature the poor motor wont be getting there also - result
abnormal wear and tear.

Ray

Perkins wrote:

> Hi,
> I am about to put the third muffler in three years on my 91 Jetta.  I drive
> this car about 5000 miles a year and it sits, unused, over the summer.  Is
> that killing the muffler?  Is stainless steel the only way to go.  Does
> anyone know a supplier and the approximate cost?
> Thanks, Lloyd
>
> 91 Jetta
> 85 Crew Cab
> 83.5 Westy
> 71 Super Beetle