Hello Arc310 and dragon,
Here is my trellis details you can build too.
I used onr 54" tomato cage ($6), two pieces 10-ft EMT (1/2" diameter ($2.6 for 10-ft)) cut in half to make four pieces, and two pieces 3-ft plastic conduit (electrical or water). Some 1-ft electrical wires to tie the conduit, pipe into the tomato cages. I used whatever are available around our house. All above materials are available at Home Depot or Lowe's.
Soil:
I miss 60% my backyard soil with 40% organic mulch. Fill up 80% of 7-gal or 10- gal tall black plastic pot and put inside the clay pot that I bought about $26$ from Sam Club. Whatever size clay pot that look nice with your plastic pot.
Assembly:
I insert the 54-in tomato cage in the middle of the plastic pot. Inserted four 5-ft EMT conduits even space around the cage and tied them up together. Finally I put two pieces 3-ft plastic conduit on the top then tie them up with cage and 5-ft EMT conduit. Tara your trellis is done.
It is very simple and long last than wooden trellis.
Plant:
I like to grow only four dragon branch in center. I will pinch off all the new shoots below except two shoots on the top. When they reach over the 54"tomato cage I bend the dragon fruit branch side way and cut the top of the df branches when they reach 2-ft. I like to train them as an umbrella shape. Simple, clean and nice...
Water and fertilizer:
I water once a week normally and two times per week if the temperatures over 100 degree F.
I used organic fertilizer as cow manure, chicken manure ,egg shells, coffee ground and banana peels on the top. Some Alaska fish emulsion about 2 times a year. Or spray Epsom salt when I spray my other fruit trees.
If the dragon fruit plant too heavy on top in future. You can put some rocks on the clay pot of to counter balance. So far I do not have a problem.
I hope that can help you arc310 and dragon. Good luck :-)