Little sachets won't do all that much.
I used to work for DSG as a field tech, so every PC I opened had a fist sized silica pack, I collected these for ages and ended up with 3 shopping bags worth! Used to leave a few dotted around the car and it did work reasonably well! Certainly beats de-icing the INSIDE of the car!
But if you have a leak, even filling the car with silica won't help!