A 108 mm BB as for a double should be fine. If you wan't it to be perfect you are going to come up against the problem of ideal specs vs actual specs. Actualy check the Truvativ website and see what the specs are for the single chainring crank.
I have a Truvativ Elita triple with an ISIS spline that according to specs uses a 118 mm BB spindle however I have it setup with a 108 mm BB spindle and a 2 mm spacer and its spot on. In practice you will have a little leway.
Regards, Anthony