Hi Gil, sounds like a nice rig. My son is a truck driver and he used to drive a company '05 Freightliner Columbia with the MB450 Mercedes motor. I think his truck rotted through a cylinder sleeve at about 600k miles. They suspected the coolant hadn't gotten the proper service somewhere along the way. It sounds like that Haulmark was built on a new chassis so I wouldn't worry so much about that. I'd for sure have the truck dealer give it a good inspection. If it was serviced by a Freightliner dealer along the way they will be able to pull up those records for you too. If you buy it make sure to get the Freighliner dealer to register it in your name in their warranty database (even if it's off warranty they still register you there). When you do that they can pull up the original build sheet from FL for you for the chassis. It's kind of neat to have. Gives you all the chassis specs. And then there is a thing called "Access Freightliner" that you can register on and get access to all sorts of technical stuff for your truck should you need it.
5k hours shows the generator has been used a lot. Which is actually better for them than not using them enough. My generator guy told me the vast majority of gen set problems are from lack of use.
Haulmark is a great builder. I wouldn't hesitate to buy a rig built by them. They know what they're doing. There are many calculations that go into designing these things. They build them so there isn't too much weight on the front axle. That's why it sometimes looks like there's too much overhang on the back. It might not hurt to run it by a truck stop and weigh it so you can see the front and rear axle weights. That only costs about $9.50 and it's very quick and easy. My truck seemed to have a bit of rear overhang too and I thought it looked like it might scrape getting into driveways and such. I've owned mine for three years and haven't had any of those problems. Matter of fact my previous rv was a Allegro class A and I scraped the back on that a couple times before I finally put in new rear springs and boosted it up a bunch. These trucks have air ride rear axles that automatically adjust the ride height back there. I think there is a way to rig it up to let you temporarily raise the back all the way up. My truck mechanic buddy said he could rig mine to do that if I want. I just haven't gotten around to having him do it yet. It would just be for getting in/out someplace steep. You don't want to drive down the road that way because it messes up the driveline angles. The hitches on these things are MASSIVE so what I do when I'm not pulling the trailer is set mine down to the lowest setting. That way if I ever were to scrape it would just be the huge hitch plate and it shouldn't mess up any body parts back there. I don't have the measurements for my rear overhang but maybe you can estimate from this picture:
Here's my hitch:
Have you driven a truck conversion yet? You will love it. I'm a firm believer in this type of chassis for an rv. Keep this thread alive. I'd love to see some pictures of that truck too. Good luck.