Depending on where you're downing the Rex in question and what you have at your disposal, a fairly tall stone outpost tower or on the back of a quetzal have worked wonders for me. However, depending on your landscape and resources luring it towards a cliff to where it can't reach you is the best option if all you have on you is literally the tranqs, narcs, and maybe food depending on if you're meat or kibble taming. Just remember to be aware of your surroundings for any tame that starts a conforntAri
I would think these were gonna be harder to tame but they’re actually not that hard, my stamina and movement speed is pretty high I’d say around 200 or higher but I didn’t need a trap or any of that, all I used was tranq arrows, u shoot it once then run away for a little bit turn around quick shoot it again then run away again and shoot it again and repeat, if it starts running it means it’s almost knocked out just chase after it and keep shooting and feed it meat!
KOing one and taming isn’t a problem it’s just most of the time where ever you knock out a Rex there will most likely be other predators around that can kill it while unconscious, I would clear out the area or lure it into a different spot if you can see other animals that might interfere with taming.
If you use the bear trap strategy which is if you lead it into a Dino gateway that is shaped in a triangle and with a bear trap in the middle (Large Beartrap) and when it is stuck you must put a dinogate behind it to trap it and then knock out.
Try to make it stuck, i went on a hill that it couldn't get up and shot it with darts from the top of the hill and it was simple enough to tame all I used was raw prime meat and it takes in under an hour with no boosts or anything