The low hours on the generator are not good, contrary to what the ad implies. Onan wants you to run them 2 hours a month under load when not in regular use. This prevents issues with gas varnishing and corrosion from condensation. Be sure it starts, runs smoothly without hunting once warmed up, and can take the load of the roof A/C. It can easily cost $500 to have a neglected one put right.
Also research Ford handling issues here, so you'll know how important the test drive is and what to look for.
Jim, "Time flies like an arrow. Fruit flies like a banana."