Would BTO rendered in cast iron be less effective?

It wouldn't be sun rendered for sure. Probably would smell different too. It might depend on what you are using it for.

Seems to me that one of the commercial bait and lure makers on here “ cooks “ tails all the time to make oil ! Hopefully he will chime in !

My experience: Tail with the leather-- in sunshine (summer and winter) --in glass jars for 8 months to 1.5 years --filtered through a nylon stocking --yields a dark liquid that alone is a poor lure. But it makes a very good lure base for me. Not much odor alone so if you have some ingredients you like (I have mine) use BTO as the beginning base, add, mix and bottle for the line. I have had no significant catch difference in letting the additional ingredients "set" or "age" in the oil before using. Chemical decomposition/change will alter whatever odors you mix unless you can stabilize the batch so use what you have confidence in (salt, glycol, alcohol, sodium B., etc. etc.). My take.

I don't grind the chunks, just jar them and sell them as is, instructing folks to put it down a dirt hole.
I can't keep enough, and sell nearly as fast as I jar it. Took it off our website, since I'm out in a few weeks, once my regular customers know.

MAYBE, add something strong like a splash of Canton or White Musk??...my BTO is pretty strong smelling.

I try and keep stuff simple/inexpensive to make whenever possible as long as quality doesn't suffer.

I use a hot box in cool weather like TonyF too, they sure are handy....and bout FREE.

I "fillet" the tail off the bone so only the skin/fat of the tail drop in the bucket.
$2 electric carving knife from thrift store, come into the bone from 90*, every inch or so, then zip down the edge of the bone so the chunks fall into awaiting bucket.

When you guys say “hot box” ?...?
Thanks

Mine is a dead freezer with a 60 watt light bulb in it

and to monitor heat, I use an indoor/outdoor thermometer.....backwards, with the sensor down in the box. and used to uplug/replug the light until I put a dimmer switch on it to regulate steady heat.

same here john I got two old stand up deep freezes with 75watt bulbs no thermostat yet but I left the wires so it can be added later I use one for just tainting meat the other will be for just tincturing