Welcome to the forum and if you are like most of us you will LOVE the Travel Supreme. In response to you questions:
1) Other than the known x-bracing issue are there any other major issues I need to ask the owner about?
The X-bracing is the only real complaint/issue that I have ever read about with the TS line. It seems to be common on the larger rigs with the K2 chassis, but I have read posts about windshield problems on some of the smaller rigs (40'). I have a 38' Envoy (38DS04) without the x-bracing and have had no issues.
2) The tires are marginally old and they agreed to pay for new tires. I'm clueless when it comes to tires in this category. I'd appreciate any advice for what to buy and what to avoid.
I cannot help on where to buy. However, based on many reviews of RV owners who have replaced tires, this is the way I am leaning:
Michelin- Good tire but overpriced.
Goodyear - I would not buy because of the numerous complaints of wear problems (rivering).
Yokohama & Toyo - Seem to have many happy customers with competitive pricing. I have had great luck with both manufacturers on cars & trucks and will be looking in this direction when I replace mine soon.
Obviously there are many other tires available, but based on what I read, I'm limiting my selection to the above.
3) I will be taking it to be inspected prior to buying it. Any advice on reputable places in the Phoenix area that will do a comprehensive inspection for me?
Sorry, no help here.
4) I'm puzzled on why most of the 2004 40DS0's I've seen has the mid-coach flat screen AND a old tube TV over the front dash. What was the design reasoning for this? Would it be difficult to remove the front TV and mod the box to make a small cabinet?
Probably price and space limitations on the mid-coach TV. In the 04 time frame the flat plasma/LCD sets were still a bit expensive. A few years ago I replaced both my tube TV's (above the dash & bedroom) with LED sets. I did all the work myself in about two days. If you are an average wood worker, it is a DIY project. The hardest part is dealing with the removal of the dash set because of weight. I found a LED set that fit between the two side cabinet doors so I reduced the height of the existing TV cabinet and now everything is the same height across the dash. Since the replacement TV was only 1.5" thick, I surface mounted between the doors and it looks like a factory job. The only problem is the speakers in the new sets are in the back so I added a sound bar below the TV. The sound bar came with a wireless sub and sounds pretty good.
Good luck with the purchase and feel free to ask away,
05 TS Envoy