Planar distortion of canvas

I have received an old oil painting on canvas (6x4 feet in size). It
has horizontal wrinkles spread all over the surface. In humid
climate when it was raining in India the wrinkles had disappeared.
Once the climate became dry the wrinkles have reappeared on the
surface. I feel, it happens because the canvas gets loosened in the
humid climate and so is the paint layer. But in dry climate the
canvas gets back to its original size but for the paint layer. It
does not shrink and therefore the wrinkles resurface on the
painting. I would like to stretch the canvas in humid condition and
then impregnate the canvas with a suitable mixture to make it
insensitive to humidity. Any advise for the suitable impregnating
material is solicited. In India Wax-resin mixture is commonly used.
Any comment?

                                  ***
                  Conservation DistList Instance 13:28
                 Distributed: Tuesday, November 2, 1999
                       Message Id: cdl-13-28-020
                                  ***