I've made an awesome map on foundry that i'm looking forward to post on forgehub. i've merged boxes into the ground multiple times, (about 4-5 doors down)and they are slightly crooked. I've saw many maps on forgehub and they've merged boxes into the ground multiple times, and it was exactly straight! I've did that before but it was just luck. I went to look at the forging 101 and i've tried the mancannon idea and it works but the box isn't straight. and sometimes the boxes go crazy So, if any of you can answer my question please do so I would love it if you could contact me on xbox live, my gamertag: sSENSE
Have you tried the Save/Quit method? Just brace the box completely, grab but don't let go, and as fast as you can pause, save the map, and quit. Even if it flips out a bit it should be straight when you go back to it. Other methods require you to get under the map and leave a brace there so it won't fall all the way through.
More guide objects is always better. You can even try interlocking several walls/boxes into each other just for the guides. The way it works is the fact that instead of glitchign through just one box and ending up crooked, it has to glitch through two or three in the same place, which is far less likely to happen.
i just want to add that if you do this, do NOT touch the right trigger. it makes the rotations set to what the object currently is, not what it was when you grabbed it.