Congratulations on the first night and welcome to the JOF.
There are fans at W*mart and Amazon that use batteries and some that use 12v power. Keep in mind that if you use your trailer's 12v power, you'll need to recharge your battery from time to time and charge it before you leave home.
There are inverters that change 12v DC power to 120v AC power. If you are running one of those (plus fans and tv and DVD player) from your trailer battery, you will need to watch your 12v battery voltage and have a plan to recharge it.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.