Now that I think back, my $250+ were much heavier too. I ran 6" majority of the time but still were noticably heavier compared to the cheapy 6" carbon filters of the same size.
Out of curiosity, how do you utilize your exhaust fan/carbon filter with your tent setup and run pos pressure? Running neg pressure I can keep my fan, ducting and fliter all outside of my tents leaving 100% of the tent's real estate aside from the light. No smells gets out past the filter. Since you currently run cooler air from another room, I'll assume you must already have your tent inlet ducted to that cooler room already correct? Just let the exhaust fan and filter sit outside of the tent and let it pull vs having to push the cool air in which is creating that positive pressure in the tent. You can get a thermostatic controlled outlet for like $30 and set it to come on when the tent reaches your set temp (e.g. 81*F). Plug your exhaust fan into that controller and your tent will come on and exhaust every time the temp hits 81*F. In turn, that same exhaust fan will also pull that cool air needed from the other room every time the tent hits 81*F. Let that one exhaust fan outside of the tent pull and push all in one function every time it kicks on.