Gerry--
Chafers are not designed for reheating, they are designed to keep hot food hot. As Joe notes, reheating can take too long (and this is why their use for such is illegal in many jurisdictions; the danger of bacterial growth is higher).
If the facility wishes chafers only then I would strongly suggest reheating directly on all the grills you have, till hot, then stacking 3 or 4 slabs together and double- or triple-wrapping in HD foil and placing in a cooler packed with towels. Have everything else packed in your car and hit the road.
Since the ribs were hot when they were coolered you n eed only get to the location, set up your stuff, and get the ribs in to hold. This will ameliorate the arrival time so you won't need to get there too early.
Chafers are designed to be double-panned, i.e., two pans in the chafer excluding the lid. Put hot water in the bottom pan, place the top pan in the bottom pan, put the lid on, then light the sterno. The ribs can be unloaded into the pans shortly thereafter, when the water is hot and steaming. I would suggest leaving the top pan dry. (The water in the lower pan serves as a buffer for the direct heat.) I see no need to have liquid in with the ribs at all. The ribs can be left in the foil till serving time, or you can unwrap them sooner if you wish.
Be sure the slabs you have will fit iin the chafers you have. If not halve them befor reheating or before foiling.