RPG Maker U2U has a free demo out right now! It's just a demo for the map creation so it doesn't have anything crazy in it, but so far this is the easiest 3D map creator I've used. Something about RPG Maker just has sauce man.

As you might be able to tell, the demo doesn't have the ability to place actual interactable objects yet so there aren't any doors. Instead, I had to paint closet doors onto rectangle shapes. Unfortunately, it doesn't seem like I can get the player to be able to walk through them as of right now.

Still early days, but I'm liking what I'm seeing a lot. It has a map import feature too so you can import your MV/MZ maps right into it. That's a really nice feature. You'll probably have to do a lot of work after that but it eliminates some of what you have to do so hey, that's nice.