I've seen this done before and it is effective. The canopies are relatively cheap and give you a clean work space to control the environment. You can get sides and end doors from Amazon to fit most standard A frame canopies for not a huge amount.
* Put down a large tarp to serve as your floor.
* Install disposable drop cloth plastic over / outside the frame. Tape this to the pipework where you can to help drooping.
* Install the normal canopy material on top of this disposable plastic. This will give your plastic support but also be protected by that drop cloth plastic. Tape where you can together.
* Tape the side and end walls to your floor tarp. You're making a sealed room here.
* Install your fans on one end with filters, Install vent holes at the opposite end with filters as well. If done right, you'll end up with a positive pressure chamber so any air leaks will push dirt *out* and not let dust, dirt, or bugs into the space. There's lots of schools of thought on this. KISS works. Explosion proof fans are not needed if you're not drawing contaminated air through them, and in a pressure setup, this doesn't happen.
* Ratchet straps are your friend. Use them between supports to give more mounting supports for your roof, side panels, etc. They can help hold lights too.
* Flourescent lights are great. I recommend running a few loops of clear packing tape around the housing and bulbs to hold the bulbs in case you bump into one. Simple cheap insurance. I do it for all my lights even in the garage.
* Work space- put in a folding table *with tarp cover*, maybe a wire shelf rack or similar for storage of all your materials inside where you need them. You don't want to be doing your mixing outside of the tent. Keep all your materials at the same equalized temperatures and where you need them.
* Don't skimp on a cheap respirator. Your health is important. If you're sick, you can't be enjoying your garage, your car, or your life. Get a good respirator with replaceable cartridges. Good rule of thumb- if you can smell the solvent, you're in danger. A good respirator will fit your face and seal.
And with all this said, I still hesitate and wonder if I could just take my car body to a shop to spray instead and not deal with the hassle, but then again, all of this prep work is kinda cool so... HMM. Do you or don't you?