I hope other owners reply too as I have limited experience...
My medium-duty, Freightliner M2 with a Mercedes engine calls for oil changes every 20,000 miles for 'regular highway use.' It holds over 7 gallons of oil and has two oil filters. Obviously, oil changes are going to be expensive.
My plan is to draw an oil sample every 10,000 miles or so and send it to Blackstone Labs for analysis. Then, I'll change the oil when called for by the analysis and not on a fixed mileage or hour interval.
Other maintenance is minimal - lots of grease fittings, check brake adjustment, etc. The Renegade dealer should be able to show you the owner's manuals for the rig you're interested in to get more details. There's an initial filter change required for Allison automatic transmissions.