Hey @kushgrowbo it looks like the humidifier you ordered should be pretty good for the size of a garage. Assuming you are correct and it’s insulated pretty well in there, hopefully it will help do the trick! I have a pretty open room with two doorways that my Grobo is in, and I use a similar size humidifier. I am able to keep my humidity up to 65-70% if I wanted to if I let it run for a couple of hours. Hoping the same thing will apply for you!
Keep in mind that humidity and temperature can go hand in hand, if your temperatures are cold around 20-23C then the humidity will still be able to climb pretty high, but if you can possibly somehow raise the temperature a bit too it will increase the amount of humidity (water) able to be held in the air. Warmer air has more capacity to hold humidity.
One thing to mention, as well, is to not forget that using a humidifier on the ground level is not as effective as raising it up so that it mixes with the air a bit. If you can find a table or chair or anything to raise the humidifier up a bit, it will help. Also, if possible, a small fan blowing the moisture coming out to mix it into the air will also yield a greater result too (as far as I know)
Also, keep in mind that anything you can do to help raise the humidity will most definitely be better than nothing. There are a couple users on the forums that have a lower humidity on the regular. I believe that @Todd.grobo has said that his humidity level is often around 25% and he has had many successful grows in the Grobo.
If you can get your plant the best assistance that you can, and get her past vegetation, once you hit Transition and Flower it’s best to lower the humidity if possible. When Flower comes the lower humidity could be a benefit to prevent mold issues, which are common with high humidity!