I wouldn't rely on that 100% - I still got flats on the MTB with Marathon Plus tyres on - if you're unlucky enough to run over a nail or a larger, sharper bit of stone/flint/thorn/glass, it'll go through no matter what protection you have.
Prior to that, I'd tried Slime tubes in my Conti City Contacts - all that happened was that I got a puncture that spewed green slime until there was no air left in the tyre....
At the very least take a spare tube and a repair kit with you - it's better than being stuck, miles out either way from your destination or your starting point, on a freezing cold, wet and windy morning!