Otter, this is excellent!
Love the "muffler" idea, and really there is only one connection point where the seal is absolutely critical: the exhaust side connection to the filter. Everything else is either filtered air or clean air, really.
A leak anywhere else, and it is either sucking fresh air in, or pushing cleaned air out after the fan.
I'm highly considering this idea to run multiple tents. Not 100% sure yet, but it's definitely a better option than running 2 fans/filters. I may even bump up to an 8" fan/filter, but probably not right away.
Even better is the filter could be bypassed for the early stages where it's not an issue.