With dragonfruit it is best not to think of them as a cactus at all, but rather a rainforest plant which particularly dislikes wet feet. Plant in fast draining mounds with good moisture retention, and cover this with a very, very thick layer of uncomposted leaf litter and manure, if you can get it. Water all the time, keep the soil moisture at a good level, and keep adding the leaf litter. This should also be watered to help it break down.
If you have an old aluminum ladder, you can make the best type of trellis. Basically just run this between two massive posts (along the top) and that way you can get a lot more plant before pruning, which means more fruit and more cuttings in the long run. I may still do this if I can find a crappy old ladder whuch has a decent length, somewhere--but I'm not paying for one.
Don't plant them out anywhere they will get baked most of the day. The worst thing you can do is treat them like an opuntia, Totally different, with totally different sun exposure tolerances.
If you want to make them super healthy, give them a drink of mineral water.
The new trellises I am building will all have abandoned motorbike Tyre rims fixed to the top, which will help to spread out the growth and will help with weight distribution. That;s if I can't get a ladder. Remember the plant itself gets incredibly heavy in later years, so you want a very strong post that is very firmly secured in the ground. Struts are recommended also. Otherwise, it WILL fall over, and you probably won't be able to get it back up again without using something like a block and tackle.