Never, ever crawl under any vehicle that is supported only by a jack {"any jack},
use a jackstand{s}. Harbor freight has decent Bottle Jacks and Jackstands for not a lot of money. Also carry some sort of compressor and tire repair kit. You do havd a spare, right?
As far as it being unlikely that you will get a flat... think again, it iks not "if" but "when". I had 3 in 4.5 years and fixed/ changed them all myself. They were all on the right rear as the shoulder is where all of the debris lives and the front tire just flings it back to the rear...seriously.
Check, your psi every trip and the first chance you get replace those China Bombs that your trailer probably came with...Maxxis' are an excellent replacement.
As always... Opinions and YMMV.
:C