Pretty easy to tame a rex low level, with crossbow and tranq arrows.
Lure him in a place where you are too high to be hit, but can shoot him. Very easy to find these spots on Scorched Earth, and rex spawn near such places.
But be warry he'll flee when his torpor becomes serious.
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!
They are actually really easy tames People are always like oh build a trap oh du du du du NO all you need it’s a Tanky parasur and some tranq arowws there then just wait 2 seconds before shooting again
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.
Place 1 stone foundation near the rex you want to tame, (not too close) then 1 doorframe and door, both stone. Then place 3 stone walls around it. Add an extra layer on top of the base structure of stone doorframes then cap it of with a ceiling. Shoot the rex to get it’s attention, then run inside and the rex won’t be able to hit you, but you’ll be able to shoot it. This trap also works for Spinosaurus and dire bears.
If you're using a taming pen for rexes, build it at least three walls high. Sure you are able to keep it inside the two walls high pen, but an especially cheeky rex might climb out of it, which is definitely not going to end well for you.