I can't really quit my job, and I don't want to come up and build a crappy product idea to peddle on the internet. My ideal situation would be to help out a growth team on the side. Would this be a viable option?
In my experience, you could benefit from reading a solid textbook on the topic. But more importantly you need some sales experience - I mean direct person to person stuff, that is where you get immediate feedback on your pitch, etc. Sales experience in turn gives you an understanding of how marketing supports sales. What many people call marketing is nothing more than a shotgun approach to advertising.
I've read a book I really like called "Marketing for Developers": http://devmarketing.xyz
True. Writing an eBook is a lot easier than software.
But what I really want to do is help out an already established website with existing traffic. Rather than build my own from scratch.
So many open source projects would benefit from some good marketing.