Better/safer to have only one w/d bar? Or none?

I towed my trailer without the Equal-I-zer bars a couple times. It towed fine but was more sensitive to passing semis and the like. Your trailer doesn't appear that it would be too much for a newer half ton. I have a similar truck and would go without. If you haven't already, consider airing truck tires to max, assuming they are the OEM P-metric.