I have a 350 and a 150 in my garage in N. California. There are actually some very solid advantages to having large tanks in the garage...not the least of which is the increased accessibility when performing water changes. However, there are some special management considerations with respect to water temperature. During the summer, my garage can hit 92-94 and if we have a hot spell for five days or so, the water temp could exceed what I consider to be safe upper limit of 85F. So, I do things like turning down the heater settings so that the tanks can cool more at night, removing lights from on top of the tank, performing wcs with cool water and adding ice on occasion. This summer, we have thusfar avoided the usual month long Indian Summer and no special actions were necessary. During the winter, I simply add additional heaters and have insulated around the garage door. It is quite manageable.
Finally, don't forget that most garage floors have a negative incline as you move toward the garage door and you will have to shim your tank stand. In my garage, the incline is approx. 1"/8 ft.
