If this is a 'boat cover' and doesnt need to be 'pristine' ....
just 'functional', You can use 'fast cure' 3M-5200 instead of stitching ... and the repair will be 'permanent'. Cut the patch to overlap 1/2" then ..... Just use masking tape to prevent the caulk from squeezing out to where it would be 'unsightly', apply a thin layer of 5200 on both sides of the seams, press together until set, etc. The seam overlap would be the same as when you sew. Once the caulk 'kicks' then carefully peel away the masking tape ... very carefully preventing the caulk on the masking tape from coming in contact with the cloth. This will make a flexible 'never ever come apart' seam. You can use flat seams or felled seams. If making 'complicated' seams just steam iron them flat before you add the caulk. Since 3M-5200 is *permanent* you cant make any mistakes during the assembly as once it fully cures, nothing on earth can be done to 'change' the seam (not even "de-bond"). For long sailing passages I take a tube or 2 of 5200 to make repairs in sails or canvass; I leave my sewing machine at home. www.sailrite.com/FAQ?search=5200