Ok all Im going to start with a DISCLAMER this setup takes a little work I feel that you need basic knowledge of soldering and be tech savvy its not the easiest setup so with that being said if you feel comfortable to do that I think the payoff is worth the work it is a pretty sweet fan setup.
Alrighty than there is two different setups a 25MM and a 30MM both install the same just choose what size you want to go with, the 25MM setup will get the job done if you want to go with smaller and lighter they work ok at about 80-100% but the 30MM setup works great with plenty of power I'm usually between 50-70% and the 30MM fans seems to run smoother but it just might be that the 25MM fans were pretty cheap so you might be able to find something better.
I used two 12V fans is series instead of 24V fans with this design mainly because I already had a few 25MM 12V fans already so that is what I started with and than I decided to go to 30MM so I kept it the same also it seems way easier to get 12V than 24V fans, you defiantly can go with two 24V fans in parallel and it would probably be easier but I opted to go with dual 12V fans in series instead, just refer to the pictures I think its enough information. I did already have the connectors from RC hobbies over the years and a capacitor I striped from some electronics I had laying around so you might have to make a trip to the hobby shop or come up with a similar setup. I used the capacitor too smooth out the fans and to help the startup (pay attention to the polarity) if you do the two 24V fans in parallel that is probably not needed but won't hurt. Also very IMPORTANT I used a Neoprene washer to insulate the extruder from the arms I picked it up from ACE for a few bucks I believe it was 2.5"X1/8 the burn point is around 260 degrees it works well otherwise it will for sure melt the arms.
Also if when you first try it and your fans or 1 doesn't spin reverse the polarity on 1 or both it won't hurt anything if they are reversed it just won't spin, test it before you button it up.