Hi
There are a Few ways to fix it.
1) Tear Mender Glue (Latex Adhesive) Just take a pc of Cotton Cloth same as the canvas and glue it on. Dries fast and will not stick to you. It is Water proof and VERY strong. I sell this in a 2 oz bottle. It comes with the screen kits that we sell for the pop top westi on my web site at www.fanchers.com Click on VW stuff.
2) Tear Aid, Like a Clear Tape I put it on my back egde of my canvas that pokes out of the back of the pop top and got a line of small holes. Patched it inside and out and its been on there for4 years. We Or I sell it by the foot if you need it.

I dont sell either on my website but you can call if you cant find it locally. Ive actually seen it at Wal mart home depot lowes and others for the Glue. as for the tape style tear aid cabelas and camping, fishing, hunting and hiking stores tend to have both.
Hope this helps.
Im at the campground now, Sunny and Breezy, Nice Day to camp for a Fathers day weekend.

C-ya Jonce

From: Loren Busch <starwagen@GMAIL.COM>
Date: 2008/06/13 Fri AM 11:37:28 CDT
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Pop top canvas repair

 RE: Pop top repair
I had good luck with a tear at the corner of the screen on my '90 using
'iron on' patches, cut to fit the situation.  A hot iron on one side and a
board held to the other side, patched both sides for strength.  Sewed it
first, then the patch.  Has held fine for about three years now.