When did you pitch your yeast and how long has it been vigorously fermenting so far?? What kind of yeast are you using??
The smells emanating from the fermenter are not necessarily an exact indication of what you will end up with at the end of fermentation and after bottling/conditioning/ageing. Porters are often pretty funky smelling during fermentation, anyway.
Firstly, it's probably going to be advantageous to just leave the beer in primary for a minimum of three weeks from pitching. Then check FG and bottle, if stable, and condition at room temp for 3 weeks.
If, after a three week warm conditioning followed by a few days to a week in the fridge, the beer still seems to be in need of more time to condition, your garage storing option sounds like it'd be a good idea. Porters are one of those beers that really do benefit from extended ageing/conditioning before they come into their own and start tasting optimum.