The advantage to the garage is you can provide greater air circulation that this will discourage fungi. The darkness is not an issue. If the garage is on the cool side so much the better.
The black parts of the bulb are not something to worry about as long as they are the outermost parts. These are the leaf bases, and their turning black is a natural process. If the black starts eating inwards then you have worries.
I overwinter my plants in an unheated cellar where the temps are seldom higher than 45-50F and occasional freezes happen. There is very little light. I just leave them in their pots after trimming black parts off. I keep the pots just moist, and not in tray water. I have never lost a plant using this method.
I have a friend in Brazil that grows VFT's and Sarracenia. His temps. never get much below 55F and the plants continue to grow over the winter, but at a much slower rate, and produce smaller leaves and traps during the short days of their winter. With the increasing daylength of spring, the plants resume typical growth. They prosper for him, increasing in size from season to season and they flower and fruit normally.
One of the most important issues of dormancy is the photoperiod. Maintaining the plants under a natural daylength photoperiod (or less daylength, as in complete darkness) will go a long way toward maintaining their health. When the plants are given a long day photoperiod in winter, they try to keep growing, exhaust themselves and die.
I never trim any leaves that are not black. Well grown plants will maintain their leaves throughout the dormancy, and the nutrients contained in the leaves will assist the plant's early growth in the spring as well as provide nutrition by translocating and breaking down starches stored there during the dormant period when there is little or no nutrient uptake from the roots.
Temperature is a secondary consideration: cooler is better, but obviously not essential. Remember to check your plants: if they continue to grow, even if slowly, you must provide them with some watering but do not leave them standing in water until active spring growth resumes.
