Weatherstripping Seal

im looking for a cheap solution to sealing the cracks in my rear window for my 65 mustang coupe.?

I just need a fix to last about 6 weeks. I do live where it rains and water does get through the cracks. Is there anything i can put on my cracks on the outside(preferably) or inside(if i absolutely have to) to seal up my weatherstripping from the rain?

http://www.permatex.com/products/automotive/auto_adhesives_sealants/sealants/Permatex_Flowable_Silicone_Windshield_and_Glass_Sealer.htm

1AAuto.com Fix Rubber Weatherstrip Seal Door Jeep Grand Cherokee 1999-04