I found a spot on the SE edge of the Volcnic biome that has am "island" with a tiny moat like spot. Any area on that edge of the map will work. The "island" is about 2x2 foundations and has a nice straight run path on one side and a small hill on the other.
Pull the Lava golem out of the volcano carefully to not bump the bottom of the skiff as then you will drop it under the map. the golem itself can dip under the terrain a bit however. You need to go out the largest crystal tunnel that leads to the big lava lake. and then fly over the lake to the south exit from the volcano. Once you Arrive put it down a ways away from the 'island'. Park the skiff behind the hill.
You need to have built a large hangman that you can grapple or dangle a spider just above the top of the golem's head. This will freeze the golem in place. Then just use a seige cannon on a Mek to K.O. it. You can build a metal trap using dino gates, but you end up with a golem punching them and have to time your shots.

Tried to tame one with stone, ended up taming a Giga while waiting

Rockets no longer knock out Rock Elementals!

For some reason, after the latest update, X-rock elementals (haven't checked other variants) are no longer tameable. Whenever you knock them out, they don't eat and don't have a taming bar. Forcetame also doesn't affect them, so I believe it's a glitch

To tame these turret soakers I’d recommend getting four metal gates 5 pillars 3 ceilings and 3 walls. For the trap and the pillars are supposed to prevent the golems rocks from hitting the cannon. AIM FOR THE HEAD