Last night (it was night for me) I was watching Hackio's stream, when he started making a model. I have always had trouble with model importing, so I paid close attention. Sadly, the stream buffered most of the time when he was doing that, and a stream archive hasn't been uploaded. I mostly had to guess how he did it, but I did get the model in Whitehole. After scaling it by 5,000 (it was really small) I noticed the animated texture was not showing. There was plain white instead of animated lava.. Weird.
I tested the level and half the collision was missing, some was shifted (mario went halfway through the ground) and there were random walls in seemingly random places. After asking Hackio, I learned that scaling can break collision, the most I should scale is probably 500. So I went in Blender and scaled the model up. When it was ready, I exported it as Extended Wavefront (.obj) and edited the OBJ and MTL to rename the animated texture None_SandRiver.PNG.001 to SandRiver_v. After a lot of trial and error, I got obj2bdl working, I converted my OBJ, made its collision, and packed the .ARC with the BTK from Hackio's BTK tutorial on K64. I compressed it and added its entry to ProductMapObjDataTable. In Whitehole, I placed the now huge VolcanoIsland and a sling star with a path (so I could look at the lava inside the colcano from ingame). I placed a Huge Used Block so I could stand (the floor code was Damage Fire) and tested the level. I got a crash.
If you need the model and BTK, or a clarification on something, I can give it.
EDIT: ended up getting help on Discord. I still don't know what is wrong with what I did here. Could anyone help?
If I made an SMO level editor, would you use it?