Thanks everyone for all the input!
As mentioned I have a Westfalia so I appreciate that removing the rack out of the gutters is inconvenient.  For me though drilling into the fibreglass is not desirable unless absolutely necessary.  I hate putting holes into things that didn't come with holes.  Or doing something that can't be undone.  I was also worried about weight - if it would cause stress and crack the top.
But I have used foam blocks in my younger days and secured it fore, aft, and side to side to the point where it wouldn't budge an inch.  All that changed with a good thunderstorm.  The combination of a little moisture to lubricate and strong cross winds had that thing swaying about six inches back and forth.  Never again.
Jeff

> Date: Tue, 21 Aug 2012 10:32:00 -0500
> From: jim.felder@GMAIL.COM
> Subject: Re: semi-OT: questions about carrying a canoe
> To: vanagon@GERRY.VANAGON.COM
> 
> My friends and I ALWAYS manage to tie down laterally. Simple for-and-aft
> lashing is not enough; I can put you in touch with people who have skidded
> a new boat down the interstate at 70, and they are lucky that's all that
> happened. The westy has metal cleats that can be use, one strap pulling to
> each side. On other cars, including tintop vanagons, we pass the straps
> through the car with the windows down and then roll them up when the boat
> is secure. You can also close the back doors on the straps in some cars,
> but more water gets in if it rains than just having the windows cracked.
> 
> You can't do it on a westy because of the screens. But as I said, with the
> cleats up top, you don't really need to. I make sure my straps (cam locks)
> share the load through several cleats, never just one.
> 
> Jim
> 
> On Tue, Aug 21, 2012 at 10:09 AM, Dave Mcneely <mcneely4@cox.net> wrote:
> 
> > ---- WELLHOUSE MAX <dimwittedmoose@CFU.NET> wrote:
> > >
> > > My final point to this subject is that the cheapo kits have NO way of
> > > lashing the canoe laterally to prevent cross winds from blowing the boat
> > > off the van.  YMMV
> >
> > Well, as one who has used foam blocks to transport a canoe (not on a
> > Vanagon), I can say that lateral lashing is certainly possible, as I have
> > done it.  Every canoe has thwarts running gunwale to gunwale.  Everyone can
> > make use of lines from the thwarts to automotive pillars.  That might be
> > more difficult on a Vanagon (or any van) than on a sedan.  The foam block
> > kits as sold are completely inadequate.
> >
> > But, a good rack is far better, and I gave up using foam blocks after an
> > experience that made me believe I could lose the canoe despite lashing to
> > the best of my ability.  mcneely
> > >
> > > DM&FS
> > >
> > > On Mon, Aug 20, 2012 at 11:37 PM, Gabriel Hourtouat <
> > ghourtouat@gmail.com>wrote:
> > >
> > > > "...is it generally recommended to use the bars that fit into the
> > > > gutter, or to drill into the fibreglass and attach directly to the
> > > > poptop?..."
> > > >
> > > > Jeff: No bars required -- foam blocks suffice.  Google search "canoe
> > > > on westfalia" to get some ideas.  One example:
> > > >
> > > >
> > > >
> > http://www.google.ca/imgres?imgurl=http://www.westfalia.org/community/gallery/files/2/7/5/3/8/van-canoe.jpg&imgrefurl=http://www.westfalia.org/community/gallery/showimage.php?i%3D1108&h=450&w=600&sz=48&tbnid=My5IwTtyiFTJyM:&tbnh=90&tbnw=120&prev=/search%3Fq%3Dcanoe%2Bon%2Bwestfalia%26tbm%3Disch%26tbo%3Du&zoom=1&q=canoe+on+westfalia&usg=__elNOfuXmbwn1CpjdqcezgAzDPkk=&docid=q8iXpjtORH9CXM&hl=en&sa=X&ei=jgszUKHpHsfrygGW_4HIBw&ved=0CFAQ9QEwAg&dur=495
> > > >
> > > > I would choose some other position for the foam blocks so that the
> > > > canoe is not touching the van directly.  Could consider letting one
> > > > end hang off the back of the van sufficiently so that the other end is
> > > > in the luggage hold.
> > > >
> > > > Or could consider strapping a bar across the luggage hold to gain some
> > > > clearance or stability with the canoe resting on foam blocks at the
> > > > rear end of the pop top, depending on canoe length and beam.
> > > >
> > > > gabby
> > > >
> >
> > --
> > David McNeely
> >