cold return air vents
I have decided to attempt slicing into the road barrier in the crawlspace and resealing any leaky spots in the main branch duct. I have two further questions: 1. The large crossover hose from the main branch duct to the duct in the other half is connected to a large hole directly beneath the ac evaporator core, which I feel leads to unbalanced air distribution between the two ducts. Should I keep the large crossover hose, or would I have more efficient airflow by removing the other tin branch duct and installing new 10" flex ducts from the main branch duct to each outlet on the other side of the mobile home marriage joint? and:
2. I feel there is a need to install a return air vent in the room farthest from the air handler, but I have heard it should be installed at the top of the wall if you have floor vents. I have also read it should be a minimum of 10" flex duct. The living room area has large vaulted ceilings with no place to hide a duct. Would installing a return register at the top of the wall and running a flat duct down the inside of the wall connecting to a 10" duct running under the floor to an outlet in the air handler be feasible? I know I am being a pain, but I have been an auto technician for 25 years and will attempt to tackle anything home-related as well, but I also know to ask more experienced people for advice when it is possible. I repair vehicles everyday, but there are people who work on hvac everyday, too. Thanks for any input!