Trouble Closing a Seal Line Map Case

[Chip]

I recently got a 12"x16" clear, plastic map case by Seal Line. I can't get the zip-lock-like closure to close. Seal Line suggests applying Vaseline, which I don't want to do because I think the Vaseline will trap dirt and make matters worse. If any of you are familiar with this map case and provide hints on getting it closed, I will appreciate it.

 

[recped]

Maybe a silicone lubricant would help.

Is the trouble indoor or outside? Those heavy duty zip-locks can be annoying when it's cold.