One big complicating factor is that I plan to use FB paper and I will have to adequately wash the prints in whatever sort of tube system I wind up using unless I come up with a better way of washing the prints.
You can't adequately was FB prints in a tube. The paper base absorbs fixer and cannot be washed throughly when in contact with the back of a tube. That includes tubes with ribs.
There are some others. Certainly there are enough
of that size tray available. I've an issue of Camera and
Darkroom which details the development of large prints
using a single tray. I'm not any way near 20x24 but I
do use a single tray.
I've made the method very convenient by using one-shot
chemistry. No stop is needed and a Single very dilute fix
yields Great LE. The same one tray can be used for
washing though that implies a few at the most
prints per day. Dan
Yes. Its difficult to get water moving around the back of the print. Also pulling a large FB print from a tube is more difficult than RC, plus as you know there is a significant difference in the time required to wash fiber compared to RC.
I would develop, stop, and fix in the tube and wash in a tray. You can use a Kodak tray siphon with the tray sitting on your kitchen counter if space is an issue.
I have been reading the thread, and though I have no experience in processing prints so large, I have a suggestion. (Worth what it costs)
You said you are using 8" PVC and need a tray for it. Have you thought about using the next size or two larger (10"?) and cutting it 1/3 length - wise to provide a tray? Of course you would have to somehow cap the ends, but it would seem to me to be cheaper than Stainless Steel and if nothing else provide a "prototype" for the SS trays you mentioned.
Good Luck, I'll be where you are by this Fall if my replacement bulb idea for my MVT 57 works!