The rule of thumb is the 'New' Spare goes on the outside dual. The reason is road crowning, since the 'New' tire is most likely larger in diameter. If placed on the inside the idea is that the 'New' inside tire will take more weight than it is rated for. In my world in the trucking industry this was the common practice if tires were not replaced in pairs (They usually were). If your spare is worn, it would be good to see what tire has visibly more tread and put the one with the least on the inside. As far a rotation direction, I think this is Poop. I have run tires forwards/backwards, etc... and have seen no consistant magical advantage to the direction of rotation. I will however comment that if your left front does show some signs of feathering or odd wear, rotate it to the right rear position (outside)(Reverse rotation) and the odds are good that you will see the treads wear even out. Duallys, well replace in pairs is a recommendation. Of course all of this theory goes out the window when you run tires with the directional rotation arrow on them. Keep in mind the your "spare" will most likely only be used in the unlikely event of a catastrophic tire failure when you have no choice but to replace it and to get you to the nearest place for a replacement tire to be installed, not typically for the duration of the tires life, so position and rotation direction probably will not make any difference anyway.

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07.5 3500 Quad, SRW, 4X4, Laramie, Leathered, Dark Metallic Gray, 6.7, 68RFE, 20K Reese, Ride Rite's, 2 Viair air compressors, Bully steps, Kleinn Locomotive air horns (5 in all), Billet polished locking fuel door, 'A' pillar mount Auto Meter Pryo, PML X-deep trans pan
06 Durango 285 RL 5'er Lifted by KZ