For hot holding roadside or event vending we use Camp Chef stoves (Costco) with six inch spillage pans (water) and four inch steam table pans (product). The HD inspectors love them cuz they hold at a high temp. But that also means you need fast turnover. The best thing is that they break down and I can fit 9 wells in the back of my Subaru.
The "Daddy" in Smoke Daddy's Barbecue