Nice trick, I'm sure it works (can't see why it shouldn't!)
A simple way to keep things cold is:
- Dig a hole in the ground (in shade, ie. under a car or a tent)
- Put a large pastic bag in the hole
- Fill the bag with water (cold! not hot)
- Put the beers in another bag and put it in the water
- Cover the hole thing by something (ie. a waiters-tray)