Do they make all season super singles?

Yes, but they still aren't as good as standard tires in the snow. I've driven both, and SS's were a nightmare in the snow. Oh and just wait until you experience the joy of chaining up SS's.

 

Michelin makes them. Same tread pattern as an XDN2, but in a super.

 

Narrower tires are better in the snow than fat tires.
Weight distribution on fat tires leaves them prone to less traction in any direction under those conditions.

Are there ANY advantages to super singles?

 

Weight... 400 pounds lighter per axle.

I will agree that there is a slight traction gain for duals over SS... But I haven't had any problems running SS on snow and ice. I run from the rockies to the mid west amd back every week, and often times when most everyone else is parking because of snow or ice I'm still trucking.

 

6x4 or 6x2?
Lockers?

 

6x4... inter-axle lock, no diff-lock... But I rarely use the inter-axle lock other than when I spin a tire when trying to get moving from a stop.

 

Rolling resistance. Only two sidewalls flexing instead of four per wheel tire combo.

 

Be careful going into any checkpoint with super singles...

One flat or audible leak and you will be OOS. Good way to ruin your PSP Score for years to come. Always try to keep your PSP Score as low as possible.

 

Calling 400lbs lighter per axle isn't exactly an apples to apples comparison now.. Maybe if going from tall 4's on steelies to 445/50 singles on aluminum, that's possible. But all aluminum duals on low pro 2's to 445/50's on singles, according to Michelin your losing 660lbs total..

More if running steelies..