Adam,
The trap assembly is installed the same way
as it would be in your kitchen sink.
I also replaced the complete assembly with a new one in
my westy.
The problem I had was that the inner stainless steel screw/strainer
(the one that you see from the top of the sink)
was so stuck to the plastic part underneath with 10 year old
crud (and the plastic probably also shrank) so that it wouldn't unscrew.
If that's your problem, you should take out all the shelves
and drawer from the sink cabinet, and get a pillow, and make
yourself comfortable on your back. Use a hacksaw blade
to notch the plastic part  underneath the sink to release
the tension. Then you can unscrew the top stainless part.
(if you do that, be careful not to cut too deep and damage the
 stainless steel screw/strainer threads).
You can also try to use a heat gun to warm up the plastic part
under the sink to soften it a little.
I used a pair of needle nose pliers to hold the
stainless screw/strainer in place from the top, while unscrewing
the plastic fitting underneath the sink.
Good luck.
Harald
'90 westy

----------
> From: Puzerewski <Puzerewski@EMAIL.MSN.COM>
> To: vanagon@GERRY.VANAGON.COM
> Subject: P-trap removal
> Date: Thursday, June 01, 2000 6:13 PM
>
> Can anyone tell me how to remove an old ptrap without destroying
something??
> I do not want to bust anything else on the sink!!!
>
> ADam Puzerewski
> 81 westy