I have a 2007 Thor Challenger
I bought my 2007 Challenger unused (but three years old) from my local dealer. I've been very happy with it! A few details may be helpful for you.
Nearly 50,000 miles so far. I have the F53 chassis and it's been trouble-free. The tires were getting thin by 45,000 miles and were replaced. Insofar as the chassis, the only other expenses have been oil changes and lubes and a chassis battery last year, plus one transmission flush, filter and fill. I've become a fan of the Fort F53 for certain.
I've driven from sea level to a bit over 10,000 feet and never felt that I might need to get out and push. Camped in hot summers and as cold as single digit temperatures (she struggles to keep up with the latter, but we survived and it wasn't all that bad - had frequent visits to the propane guy, though.).
The most bothersome coach repair was to replace the main entry door lock (the so-called plunger broke and left the door completely unusable. While I was inside. I had to climb out a window to escape. Fortunately it happened in my driveway instead of 500 miles from home! Removing the defective lock is reminiscent of a root canal - it's pretty forceful. I replaced it with a version that the dealer said was upgraded from the OEM part - it allegedly has a steel plunger instead of the pot metal part in the original part). Various screws have given up the ghost and have been replaced with alternates - usually a larger screw with some beefed-up connection areas in the coach. One sink and all faucets have been upgraded, mostly to stick-house equivalents. Two faucets failed and the 3rd was replaced as a precaution. My wife always hated the cheap plastic bathroom sink; I bought a much nicer cast iron one at a big-box home improvement store on sale and it's placated her.
One double-paned window shows signs of internal moisture and will be redone sometime soon. I don't think this is unique to the Challenger.
A couple of electrical switches have been replaced after they failed. And the cheap Chinese light bulbs have proven to be short-lived and have been replaced by hopefully-higher-quality Chinese replacements.
My personal observation is that the basic coach is very solid. Some of the accessories, especially faucet sets and sinks, are pretty cheap compared with stick homes or even higher tiered rigs, but they're replaceable and it's not hard to do.
My brother and his wife have an older Newmar diesel rig. Its components are higher quality, except for the ones I have already replaced on mine. The air suspension offers a more civilized ride. The noise of their rear-mounted engine is subdued compared with my underfoot Ford. But I don't feel compromised in any of those areas. And his bedroom is heat soaked after a day on the road while mine isn't. So it's all a compromise.
My wife and I agree that our floor plan fits us better than anything we've seen so far at RV shows, friends' rigs, etc. THAT's the most important factor in my opinion. I've been very pleased with our Damon/Thor, especially so when considering the price point. for my money, they pack a lot of value and experience into their products, but the prices are relatively attractive. I definitely would consider Thor again if I were in the market, but I have no such urges right now.
Good luck with your decision! I haven't looked back with any regret.
Coyle & Sue
Cassity (Labrador) and Rylee (Standard Poodle)
2007 Damon Challenger 355; 2003 Element toad