I'm not familiar with this brand at all.. but what I would be extra cautious looking for is any sort of water damage. If it needs new windows and vents - these are all great places for water to get in. And water damage, especially in typical sticks-n-staples RV construction can quickly weaken walls, floors, etc. Thankfully, if its been in AZ, it doesn't rain much (that's where we're currently at with our new-to-us 1961 bus conversion).
Walk strongly through the unit.. does it feel solid? Are there any soft or squishy spots? Eye the unit up and down, and look for any buldges anywhere on the walls, inside and out. Pay particular attention around windows, and below. Press on all the walls and make sure they're consistent throughout. Look under cabinets, etc.
If there are any soft spots anywhere... any peeling of wall paper/paneling/etc. - walk away.
The entire RV market is soft right now, so there's no need to jump on the first good deal you encounter. Go visit lots of units for sale, and get a very good idea of what you want. You'll learn a tremendous amount about each unit you look at - both about trailers/RVs and about what will work for your situation.
And wow... 270,000 miles on a 2003 seems high... that's over 30k per year. Was it used in a commercial fleet previously? That could be a good thing, depending on how well they maintained their fleet. Diesels are built for heavy use, so it's not as concerning as with a gas vehicle... but could be worth taking to a mechanic for a thorough inspection. What's the condition of the tires?
As far as it being a good deal or not.. run the truck through KBB and Edmunds for its value. Do a search on the trailer brand to see what others similar are selling for.
But it really comes down to.. does it work for you? Is the price in your budget, and are you prepared to take on the maintenance costs of a high mileage diesel and the known repairs needed on the trailer?
Best wishes,
- Cherie