Hello I have a 2007 40x32 doublewide and the supply side of my system is so leaky and I am sure it is in spots that I can not see. I have sealed every floor register the best I can and its still blowing out from the underbelly like there is a loose pipe. Anyway on to what I want to do. I have a 2.5 ton Heat Pump and I am using the stock air handler that came with the home. I want to go under there and make a connection under the air handler and connect it to 14" round duct along with a 90 elbow to straighten it out and run about 25 foot of 14" round metal duct. I want to add a 8 or 10" reducer and about 5 more feet of 8-10" metal duct to the tail end of the 25 foot of metal. I want to run it at a 45 angle cross the crawlspace. I want to use flex and connect take offs to the round metal 14" suppy line. I will be using the existing floor returns that have been cut and just getting access to them under the home and flatting them out or removing the aluminum duct in those spots with regular floor returns then connecting the flex take offs about 6" to each of the 9 floor registers that have to happen. Does this sound like a good figure? I have a return that is a 20x25 I installed myself when I first moved in as I hate the mobile home setup. Please let me know what you guys think. Here is a very rough setup I was thinking. the square areas are floor registers. The long thing is a rough drawing of the 14" supply line and a 8-10" tail end joint. I am going off just guessing here but could use some advice. Thanks so much!