Make a trapper boat from metal. 2 walls high all the way around then a ramp for the rex to walk up. Lure it in with a bird or by foot. Then it's safe for transport and taming. Can tame over water and have no worries. Take 2 walls down and walk out when done.
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