My new (old) 1990 Tracker has a very well made custom boat cover.  The only problem is that it is not waterproof.

Can anyone recommend a product  that I can can use to make the fabric water tight?  For what it's worth, I don't think the fabric is cotton.

http://www0.shopping.com/xPO-Marykate_Fabric_Waterproofer_32oz_Pump_Spray  

Haven't tried it myself.

LM,

Check with a local canvas shop - they will have something good. It's sold by the gallon: the key to sucess is soaking the canvas in it and then air drying it. I have done mine a couple of times. West Marine, and Boat US also sell it. Don't get the spray bottles as it will cost you a fortune by the time you are done. I used a paint roller to apply it.

There are a lot of different sealers out there.  It would be beneficial to know the material in your cover because some sealers are material specific.  I get mine from Aurora Canvass in Battlefield MO.

Alot has to do witht the type of material. I used to do canvas work for 10 years. Most materials are acrylic coted which is water proof its self, but when they get dirty the dirt transfers the water through. If it is an acrylic mixture I would wash the cover really good with soap and water and get the dirt off let it dry and do it again.  Think ofit like a tent its waterproof until you touch it with your fingers and then the water comes through. Just try cleaning it really good before spending money on the waterproofer.  I even had to preasure wash a customers cover but it was fine afterwards.

Good luck.

Many thanks guys.  Since the previous owner was a pig, I'll start by pressure-washing the cover before I take further action.  I don't think the cover is made of cotton, because it doesn't seem to have the flexibility and softness of cotton.  On the other hand, I know as much about fabrics as I know about Quantum Physics.

Compare the cost of the waterproofer to the cost of  a new cover.  It might be worth to make the little financial step to a new cover.  Chances are the cover is old and will need replaced soon anyway.  The stuff in the link above is $22 a bottle.  If you would have to use a lot of that, it would make sense for a new cover.