I used a waxy commercial sealer on a canvas tarp that I put over my
trailer, and it didn't seem to make much difference, other than perhaps
on the seams.   Also, if you read the can, some deck sealers can also be
used on canvas, but I've never tried them.

Barry Armitage
Editor, Materials Evaluation
American Society for Nondestructive Testing (ASNT)
1711 Arlingate Lane
Post Office Box 28518
Columbus, Ohio  43228-0518
614-274-6003 extension 205
614-274-6899 Fax
800-222-2768 Toll-Free
e-mail: armitage@asnt.org