I can tell you the basic method for cooking low and slow,
18 Hours is a bit too long for any cut of meat.
Generally 12-16 hours is all that is needed to break down the collagen and render the fat from your rib steak.
The best cuts for low and slow are marbled cuts such as Rib eye, Pork Neck(Scotch), Brisket, Pork belly(Spare), Pork ribs, Beef chuck roast, etc.
The thicker the cut the better it will render and start falling off the bone.
You cannot slow cook a 2cm rib eye, It needs to be 2-3 inches thick.
Better still, a hole 2-4 kg joint.
Most BBQ,s will not cook low enough unless you have a Webber WSM, Offset smoker, or are really crafty with a Webber kettle.
You can however do it in a normal electric Oven,
The key is to first rub the meat with a dry rub then cook at a temp of 100C-120C (110C is perfect). Never Lift the lid to inspect for the first 4 hours.
If you use a Temp gage you don't have to open doors or lift lids for the entire cook.
You are cooking beyond "Doneness" For beef or pork you need to slowly get the internal temp up to 90-92 Deg C,
The meat may "Stall" and take many hours to get there but increasing the heat above 120 Deg C will only end in failure.
If you do it in a BBQ such as the webber smoky mountain, It all happens naturally, I'm cooking a 6 hr Pork Louisiana smoked baby back ribs right now along with home made southern style sauce on the stove.
There is so much involved and are happy to answer Q,s
Its not hard to do fall apart, REAL BBQ meat, You just need the right equipment and advice.