Well from the post above this one the inspection would be short.. nice pic of a very nice rig!
But not knowing what you are going to chase I offer a technical view where each house component is its own system. The truck portion is durable and will always be in some state of approaching needed service, if it runs and stops well under load, idles, no leaks, and the air is cold then I am done with the truck. The two biggest (cost) threats of the house are the roof and the frig. I would look a used unit three times. First fire up the frig on ac, come back the next morning, switch to gas and return again after 5 hours. use a thermometer.
The gen is an easy service and as long as it starts by the fifth attempt primed and ran smooth under load, I would take any onan at 150 hours or so per year.. Even new units need a few times a bat to fire depending how the fuel is piped in.
Air is either cold or not. Measure the discharge temp after 10 minutes and note the external air temp also, humidity would be a nice touch to know.
Pull the wh rod, I would rather see a slight to medium used one opposed to a brand new one.
Put water pressure to it check for tank and line leaks. I would also want to see under the bed if the design has the water tank and wh there like mine. Bring a thin inspection light, thermometer, a extentsion rod mirror, and a small batt screw driver.
Finnnaally..... I would tell the seller the sale would be subject the roof being serviced (caulk check and repair) at my expense at an agreed to rv business. Great time to have the servicer do a walk around for delam.
Settle on a price, buy it, and take it to a truck dealer and have it serviced.
Change the genny oil and plugs, flush the hw and add a new anode.
The rest is house keeping....
This whole run up would only add 300-500 to your price. Oh, take a stiff lip detail person with you....
I am free on Fridays, you buy lunch...
L'IL Foot" 2014 Sunseeker 2300
"Harry" the JK toad in the mirror