Is this a good Class C?

The miles seem fine to me.

The first thing to do is go to nadaguides.com and under the RV section find the make and model and check the price. Forty eight thousand miles is not a lot of miles, so it has a long life left in that engine. The more important issue is how was it maintained. Was it covered? If the roof needed to be resealed then was their a leak? Probably. Look inside around vent frames and look for a brown stain line. Especially check the overhead cab are for leaks. A rig thats been driven is much better than one thats sat for 8 years. Check all the appliances, especially the refrigerator which is a spendy item. Look for documentation of maintenance and oil changes.

It's a THOR, there's much better out there.

An 8 yr old rv is an 8 yr old rv. You could hire an expert to do an inspection for you. Probably a few hundred well spent.

At 8 yrs old it depends on how much time the previous owner put into maintaining it plus...did he know what he was doing and did he use the correct products ?

Keep in mind that water will seek the lowest point to settle or exit, however a leak in the front passenger side could travel and exit in the rear drivers side. It would depend on how it sits when parked most of the time. That happened to me.

Inside: Look for signs of leaks (water stains or re-painted areas) inside cabinets using a flashlight as well as your nose. Beware if an rv is all opened up to air out when you go to look at it . Most of the time a closed tight rv will have an odor from dampness or mold.

Exterior: Feel the exterior for soft spots by banging on the walls. If it has a rear ladder, check the mounts for dried caulk. Rear wall replacements are common enough to be a concern in any rv.
Climb onto the roof and inspect all the things that have caulk. Roof vents, vent pipes, antennas, all seams should be clean and smooth not dried and cracked etc.
Cabover leaks can occur because the top front cross seam takes the most abuse . Check windows and clearance lights also have tendencies to leak. Some people put a bead of caulk around the exterior gaskets of the windows as a precautionary measure as well as the glass in the entrance door which show signs of leaking at the bottom where the door meets the sill.
Check the floor for soft spots especially near the entrance . Sometimes a leaking door will seep under the floor entrance area.

Maybe or not. We bought a 2003 Itasca(made by Winnebago)30 ft. Class C in 2013 with 20000 miles for $23000. So it was 10 years old and yours would be 8 with twice the miles. The 2 years isn't much of a factor. And ours has 2 slides. I think that Ford 450 chassis with the V-10 is good so I wouldn't worry much about that part of the motor home. But, I trust the Winnebago "quality" way more than the Chateau but not sure if you should pay much attention to that. All I really know about Chateau is that campground talk is that they are sort of a low end motor home. Hard to be specific about that but examine cabinets, doors, windows etc. So do you mean actually selling for $30000 or just that's the asking price? Sounds high to me. If asking 30 you might offer 22??

30 k is too high a price. Mine was 32 k, 5 years old with 4000 miles.

I wouldn't think twice about the mileage, at least it was not sitting around. Thor is not the highest quality, definitely inspect for leakage. Lift all cushions, pull back the curtains, look inside all cabinets, especially in the overhead. Delamination is easy to spot from the outside, that is a deal breaker imo.

Be wary of any RV that has coffee, dryer sheets, dessicant or other odor/moisture covering substances in it when you go look. Why are they there? Are they hiding something? Drop an overhead light or two and look up into the roof area. Clean? dry? evidence of mice? Pull the heater inlet vent and do the same down there. Any mice droppings?

Roof 'resealed' is vague. Was it just preventive maintenance? A little sealing here and there? A full re-coat of the roof?

My motorhome had a full new roof put on by the PO due to damage from a falling beam in their barn (so much for covered storage lol). They had pics and insurance documents backing it up so it seemed legit. But I do understand that a re-roof, any re-roof, is probably not as good as the original factory installation.

As to price, that's up to you. There's NADA, local market conditions, and you. Mostly it's up to what it's worth to you. Personally I don't mind 'overpaying' when I find the thing I want. I prefer that to getting a real good deal on something that's 'almost' what I want. To me, it's not overpaying if I'm ok with the price. It is, after all, my money.

Maintenance records an absolute must. IF you know nothing about motorhomes you should have an independent person inspect the coach. Their asking price is most likely what they owe on it.
Look at the date codes on the tires,not when they said they were installed. The tires may be a year old then add 5 to that.
Look for a mobile RV mechanic and ask how much to inspect, the best money you will ever spend. If a 200 dollar inspection seems like a waste of money ,a simple water leak, gone unnoticed, will set you back a ton.
A motorhome doesn't care if it is 200 miles from home or 2000. If something fails ,it was it's time. 48K on a Ford V-10 is almost to it's break in mileage. There aren't grandpa's engines that quit at 100K. That engine will go 300K with regular scheduled maintenance.

Thanks for all the replies. There is lots of wisdom and good advice here. I will use this in my search. I say search because we went to look at it today. I used to have a 37 foot Winnebago Adventurer Class A, so am somewhat familiar with what to look at.
When I got there the first thing I inspect is the tires. The four that I could see were all different makes: Goodyear, Firestone, some Chinese brand, etc. The date codes ranged from 11 to 14. For me, the red flag was already up. The slide out seal was starting to ozone crack a bit, probably sat outside with the slide extended. We went inside and noticed some black mold around the top of the cabover. They had put new carpet on the bed area. I lifted it up and saw some black mold in that area. I put my hand on the bed area and it was wet to the touch right under the vent. We saw enough. Thanks, but no thanks!
Again, thanks to all of you. It was a huge help.

Make sure everything works. And, I do mean EVERYTHING. Be fair but firm when deducting (from the asking price) for anything that doens't work properly. (unless the owner is willing to have faults repaired before you take ownership.

Chum lee