How can I keep hot food hot when transporting it?
Depending on what it is I am transporting I use different methods, and I use the same methods for both hot and cold transport.

The easiest is the towels in a box; lay four towels down in a shallow box, hanging the other ends of the towels out each side of the box, then put your dish or bread or pot or whatever in the box and fold each of the four towels over the food.  If you have hot food, lay some more insulation material over the top, as heat rises.  If you have cold food, put the box on the seat, not the floor, as the floor will conduct heat from your vehicle up into your food.

I always have a sleeping bag in my rig and I will sometimes wrap food well with towels and then open the sleeping bag and shove the food into it, wrapping the rest of the sleeping bag over the top if hot food and under the bottom if cold.  This has worked a lot for frozen foods when I go bulk shopping in the city, holding food frozen food for 4 hours and more.