I was wrong!
I took a closer look at my power usage on the Mirage these past few days. It looks like the single 20A dc-dc output converter may not handle 100% of the load all the time, even at max output. The engine running uses about 6.5A. Turn the headlights on and it jumps to very near 20A (total draw). The fan on low pulls 2-3A and another 3 on full blast. So, I may have to look at a more powerful unit (which I've not been able to find yet) or running two in parallel which I'm not crazy about.