I ran tubeless rims/tubeless tires with tubes in them for a number of years. I still carry a tube with me for emergency repairs.
Before beadlocks became popular or common this was what we did for the jungles of malaysia and thailand to air down enough to clean the clay out of the lugs, somewhere around 16-18 psi - soft enough to flex.
The tires we were running were the Deestone Bias Ply (a Thai copy of the old Goodyear military "tetris-style" tire, maybe also called the Goodyear Traction Tire, we also ran the Goodyear Wrangler MT's (radial, older style), the Geolander MT Radial, BFG AT (Radial), and original Simex Centipede (Bias).
We never had any issues with the tubes when offroading at those pressures. Below 14 psi you knew that if you gave it too much power you could tear the stem off the tube, so you would just be more careful. Usually you only needed those lower pressures in conditions where you wanted to stay on top, so you would never use much power in those situations anyways.
When we DID have tube issues was running the tires at high speed on the highway, on a hot day. So if you were running at 30psi, at 120kmh on the highway, and the ambient temperature is 40 degrees C, (104 F) then sure enough, someone in the convoy would call over the radio that they had a flat, or two.
Fixing a tube in a tubeless tire is a PITA even when you have done it a few times. Not technically difficult, but not something you want to do on the side of the highway. Carry a ready spare on the back of the truck, and a few tubes and patches in the tool box, and patch the tube around the campfire that evening.
Hope that added some value.
Cheers
Ray