We get 7.8-8.0 MPG and generally drive 62 MPH+ which is the shift to 6th gear point. While it's a good coach there are design issues.
I had to replace the totally inadequate Monaco and CareLess wiring to the switches and repair the stripped end cap on the awning. CareLess toppers don't last very long because the cotton doesn't hold up in the sun. I'm on the verge of ordering new and much better toppers. Gen starting is a problem because mine is connected to the house batteries. The battery boost will solve that but the design is flawed as there is about 42' of wire to the batteries not to mention that it's trying to start on partially discharged batteries, lower voltage and cool weather are factors. I'm considering installing a battery on the gen slide.
The Magnum charger/inverter has a number of design cost tradeoffs one being no remote battery sense. And Monaco installed it 21' from the battery and even with 4/O cable there is significant voltage drop.
I had to replace the Lipper hydraulic pump right at the 2 year warranty. I found 3 design flaws with that pump and convinced they to send me the redesigned pump. There was a minor Monaco installation problem with the Valid leveling air pump that I fixed.
The bed slide is slowing down and at least one problem is that the plywood isn't holding up on the bed box rollers so that fix is upcoming (the slideout itself is OK).
But I'd likely buy another Monaco. So depending upon the condition of the rig the above is just a heads up.
I MUST LIKE the rig since my major upgrades are: Wilson cell amplifier and antennas, PI HW 50C, battery monitor and RF Mogul sat dish.
Then the 750 watt solar has a major install. The rig is NOT boon docking friendly relative to power unless you like to run the gen.
The Dometic NDA1402 works great. What kind of refer does the unit have? The DPF filter is not a problem for me and the engine is very clean running.