They're common in rural Louisiana. We have a special baste made of onions, mustard, and oil. Pig Stand, Jack Miller's, and Tabasco all make commercial versions of it.
https://karysroux.com/product/pig-stand-bar-b-q-sauce/
https://www.jackmillers.com/product/bar-b-que-sauce/
https://countrystore.tabasco.com/products/tabasco-sup-r-sup-bbq-sauce-16oz
https://karysroux.com/product/pig-stand-bar-b-q-sauce/
https://www.jackmillers.com/product/bar-b-que-sauce/
https://countrystore.tabasco.com/products/tabasco-sup-r-sup-bbq-sauce-16oz