can anyone tell me where would the air leveling control box be located on a 2003 u320
also the sensing unit
If you are talking about the control panel it is on the console just left of the drivers chair. If you are talking about the control circuit boards they are located in the basement drivers side along with your inverter and HWH system air compressor and other electrical bits and pieces. On my coach this I as the second door from the front.
Using the Forum SEARCH tool brought up the thread below, which I believe may help to answer both parts of your question:
2003 U320 Level Sensor too Sensitive - Replace, Fix, ???? (https://www.foreforums.com/index.php?topic=18319.msg125203#msg125203)
They are sometimes referred to as the HWH "tackle boxes" since they are two clear plastic enclosures (with circuit boards clearly visible inside).