DEF has to be consumed all the time as it turns exhaust to water and a harmless gas...My regen light in my old coach used to go on about once every 5000 miles or so (once a year) and go off after about a half hour...Present coach has 10000 miles on it and it has not gone on once...Fuel mileage is better with the setup too..And although the door is on the right side..Im perfectly OK with adding the 2.5 gallon jug I buy and putting it in..not a big deal..The only coach I have ever seen with both the fuel door and the DEF port right next to each other is a Prevost...Even the driver side port for most coaches is on the rear of the coach...so you have to go back in and move the coach anyway.