Hi Miles, and my apologies for not noticing this sooner.
For my door-and-a-half cars of that type, I used Accurail's 9-panel single sheathed boxcars. They're cheaper than the Tichy (which is a very nice model itself), and if you don't want the fishbelly underframe, it's easy to replace the Accurail parts with scratchbuilt ones made from various sizes of strip styrene. For the half-door,
New England Rail Services offers a kit made specifically for the Accurail car: it's part of their Standard Car Company line.
Include with the kit are two pairs of half-doors, one with the mid-mounted reinforcement strip to match the Accurail car's existing doors (as shown above), and another with a high reinforcement strip, along with a pair of the strips only - these are for use if you wish to remove the strips from the Accurail doors, as they're actually incorrectly placed, then replace them, in their proper position, using the extra parts.
Here's a modified car with the higher stiffener strips:
You also get the necessary upper door tracks, bottom door guides and hardware, and some triangular braces that were used on some cars. With a little improvisation, you can do two cars with one conversion kit.
The modifications are most easily done on an undecorated car (readily available) and require only an X-Acto knife, a #75 drill bit and pin vise, and some solvent cement.
You could also use Tichy's standard #3017 wood door, although you'd need to section it to make it narrower and then shave off all of the latch hardware and somehow replicate it on the proper side.
For other types of cars, you can add half-doors simply by using similar doors, sectioning them down to the proper width and then adding the appropriate hardware. The Athearn doors from their 50' doubledoor automobile boxcar are particularly useful, as two of the four doors already have the latch hardware on the proper side.
Here's a Train Miniature door-and-a-half car: in addition to the sectioned half-door, both doors had to be increased in height, easily done by sectioning spare doors horizontally, then re-combining them:
A Train Miniature car done with modified Red Caboose doors:
...and a double door PRR X-28 boxcar, using shortened Athearn automobile boxcar doors:
Wayne