> I've had canvas that beaded up with water droplets on the inside but never
> dripped onto the interior. With heavy winds the result might be a pretty
> good mist to the inside.
> Good sporting good stores sell water repellent solutions for treating tents
> and other canvas / nylon items. You could apply some of the repellent. I'd
> avoid Scotch Guard (it turns yellow) and avoid silicone sprays (they build
> and collect dust).

No shameless plug here, but I am the only +- manufacturer(Busware) of
tilts(canopies) for 1952-1979 VW DC & SC's in the world?  These are as close
as I can get to the og cotton canvas canopies that VW originally made.

In any event, I treat all my cotton canvas canopies w/ a water based,
environmentally friendly treatment to help prevent mildew, mold, & for stain
resistance.

Untreated cotton canvas swells to keep the water out, but is terribly
susceptible to M & M. I have had 2 feet of snow on an untreated tilt w/ no
water inside.  As Stan suggests, do not use Scotch Guard, as it will yellow
& make your canvas brittle. I use a product called CampKote which comes in
gallon bottles or smaller spray bottles & I spray it on till it runs off &
let it dry.  Rain will then bead off the canvas but still allow it to
breathe.  Reapply as often as needed.

For custom canvases, I use a marine grade acrylic fabric "Sunbrella" which
is a much better fabric for M & M, shrinkage, non fading, etc., but is a lot
more expensive.

FWIW,

Tom