Build a taming pen. Walls should be doorframes. I suggest 2x6 and two high. Put a hatch frame as the ceiling. Lie down near the whole on the hatch frame ceiling and feed him as needed. Boring, but efficient. I use my normal taming pen and just add the other walls as he walks around, to box him in on one foundation. Then, I remove the walls when done.
It literally only took me an hour to tame a level 145 with only 50 mejoberries.
1. Gather berries and put the berries in your last slot
2. Kneel down and walk up to one of them and feed it the berries
3. Now you just follow it around while kneeling down and feeding it berries whenever it's hungry
4. Congratulations you tamed one.
Since they're commonly found in the red wood forest, I recommend only taming one if you're close to water as if you get attacked by something you can jump into the water to get away. Then when you think it's safe just go find your monkey and go back to following/feeding it.