On your sagging issue.
I was told when I built my set up
that the inline fans work better suking the blowing. Now I have and still have a hard time believing this. Everything I mechanically know say's every fan ever made blows better than suks, the only one that can through a wrench in this thinking is a engine powered prop plane, but the propeller is still designed to push more air than it suks, but the plane suks it self fwd or does it blow back pressure enough to push the plane fwd. Laws of physics, Vacuum shouldn't be greater than the force of the fan, the blades multiply it.
So what am I getting at and your issue with sagging.
They explained it to me when you push there will be dead spots, pockets of hot air, when you vacuum it removes all of the air constantly and when suking your tubes will stay up on their own. You need to move the fan at the other end and hook your tubing to the filter. Problem solved and you will run kooler 2
All of the tubing should be straight as possible too, any bends lowers the cfms significantly. If you want to run Co2 with your set up you can only run it when lights are off, you would expel all of your precious co2 out the tent when the fans were running to kool the hood. If you want to run Co2 24/7 the hood needs fesh air from outside the tent.