I have a very rare TC that I would never find again, but if I were to have to buy a TC now I would strongly consider a Northern Lite or Bigfoot. Both similar and both are two-piece fiberglass shells, like an upside down boat. They can only leak at the openings as there is no seams except where they are joined, but which they overlap so cannot leak.
They are also a 4-season camper which I wish I had. Keeping pipes thawed on cold nights is VERY difficult for summer campers.
The TCs with basements are taller, so you lose clearance and a tad bit of mpg, but you gain space that the tanks usually take up.
You said this truck had CAD, which refers to the front axle on 4x4 trucks only, so I thought it was a 4x4.
Think carefully about getting a diesel. They are super powerful workhorses and will run years beyond gas engines, but the gain in mpg does not always off-set some of the expenses of a diesel.
You will also nee to run 2-cycle oil in the diesel tank (one quart per fill up/ 30 gallons), so will add another 15 cents per gallon at the pump. The oil protects the injectors. 20 years ago diesel fuel had more sulfur which aided in lubracation. Some people add the oil, some do not. If you want 100 different opinions on this topic it will not be hard to find.