My advice would be if you want to be a trainer you need to train people. Certs and knowledge do you no good if you cant communicate properly to your client(s). For this reason I would say not to discount the experience of training out of a commercial gym chain (especially if this is all that is in you town). I will give you a few examples of why I think this is:
1. If you have a true passion for training people the quality training you provide will be evident to all...members, clients and especially other "big box" trainers. At my gym the trainers have started trying to teach kb moves, bb cleans etc. Their failure to teach such movements properly makes it clear to the client and everyone else that not all trainers are equal.
2. If you do a good job at #1 you could very quickly built a small army of devoted clients that will follow you anywhere...even a garage gym or a park!
3. Commercial gyms care only about money! If your clients are happy and stay around the gym will be happy, period. I have used rings,bumper plates, kb's, D-balls, med balls. I was even told by a "higher up" that I could have people, "hang from the rafters as long as you make your clients happy." Point being you can train quality movements anywhere, even a large commercial gym!
4. Lastly, the big box gym will challenge you in the area of articulation in regards to you own training philosophy. For example, people will ask you why you teach a kip rather than a pull-up or why you cheat on you shoulder press' .
Anyway, just some thoughts, hope this makes sense.