Hi 

I don't know what kind of plastic hoses you had in mind but be careful
if you are leaning toward PVC of similar pipe.  Pressure rating goes WAY
down as temperature increases.  On my '84, the only bad section was near
the motor end and almost all of the damage was localized to this area. 
I  had been using a sealant in the system for quite some time and it
minimized the leakage for quite a while, didn't think much more about
it.  God wad watching over me on the day it failed as we were moving
from Denver to Michigan that day.  We literally were about 1 mile from
where he had lived ON THE WAY OUT OF TOWN for the move.  I was following
with the Ryder truck (with a '81 Westy in tow of course) and saw an
immediate and quite complete dump of coolant.  Waved down the SO and got
it stopped before any damage.
  Of course it was after 5:00pm but I did have a hacksaw with me and
there was a autoparts store nearby that was still open.  Cut out the
offending area plus a couple of inches extra of good pipe,  used the
extra part for a coupling between the engine hose and the universal
replacement that I had just bought.  Connected the universal to the area
that I had removed  and viola! coolant system again.  Hose on a nearby
apartment supplied cooling media and we commenced the 1300 mile trip.
BTW that was 4 years ago and IT IS STILL in there....
Morals to the story:
	1. You may not need to replace the  entire pipe.  Corroded area on mine
was very obvious, rest was good. In fact, by the time I finished cutting
the bad portion out, there was a 1/4" hole where the rust was. seems
that the sealant held the rust together. Also, area where the cut was
made looked almost new.  Must be a erosion effect at the elbow???

	2.  Don't tow a vanagon for 1300 miles using a dolly (front tires on a
"trailer", back on the ground.)  Yes, I did take the axles out before
starting.  The problem is that the back tires wear out very quickly
because they are at a angle to each other when the front is raised
enough and you have the weight of the Westy squating the rear.

	3.  I've always played with the idea of getting an electrical
contractor to bend some heavy walled, galvanized, conduit to match the
original pipes and add some brackets...  so far, haven't need to..

Good luck 

Mark
'84 GL
'81 Westy
'82 Deisel Rabbit
'71 Ghia
'68 Circle track Bug
....