Coolers work, or in the oven works. In the oven, anything between 160-180 is probably not much difference.
The thing to keep in mind with a cooler is that technically you're supposed to keep it above 140 degrees to keep it from growing any bacteria. You don't want it under 140 degrees for more than 4 hours - within that 4 hour window is OK. I've pulled one from a cooler after 5 hours and had it still sitting at 160 - you'll be surprised how long it will hold temp in a cooler while covered with towels.