Build a 3x3 stone foundation on a raft, replace the foundation where you sit to control the raft with a stone hatchframe and hatch. Put stone walls 3x3 tall on the back of the raft, using 2 stone window frames and a stone doorframe/door on the bottom most lair. Put 2 stone fence foundations on each end of the walls, moving toward the front of the raft. Place a stone dino gateway and gate on each of those fence foundations. Place a wall 3 stone walls tall next to the dino gates, with stone window frames as the bottom layer. Place a wall 2 stone walls tall across the front of the raft. Place a row of 3 wooden ramps on the outside of the raft, starting at the top layer of walls on the front of the raft, down towards the water. Finally, place one layer of stone ceilings around the raft to the front, just before touching the ramps themselves. Now you can lure a Rex in there over the ramps, and escape on foot through the back door, or use a bird to lure it and land after it is caught.
I recommend using a scorpion to tame it, pump all levels into health on the scorpion. Then just attack the Rex but with 10 to 20 seconds in between hits, DO NOT pump anything into dm. Also this is what I use to tame literally everything, and it doesn’t even cost anything. Pls put this up in chat for everyone to go “oh that’s not a bad idea” 👌😄👍
Just tamed one I will tell you my experience, so I found one and shot it with tranc DARTS (but tranc arrows work just as well although you need a few more :)) and it kept on getting deststracted by other Dino's which made it not attack me, so after I knocd it out I killed the other animals attacking the unconchis body with my Pump shotgun and gave it raw meat and a couple of bio-toxins and boom I got Rexy I hoped this helps on your next Rex tame
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.