Closer inspection reveals that they are not identical to MWC's, so I decided to test the bugger. They definetly do NOT leak when laid on their sides, top, or any other which way. They have a rubber o-ring in the vent and the lid.
5 gallons of water in it, and played 'roll it down the hill."
No leaks from that, just some scuffing
Stood on it filled with water - I only weigh 142lbs, so this isnt the rating of the MWC's, but it held this perfectly
The next test will be:
2 gallons of water, run it over with a buick rondezvous, vent cap only.
Unfortunately its in the back of the jeep at the shop so I cant test that right now.