Everything should be just fine. As far as load goes, you will only draw what you need, and that is protected by the panel in the trailer. From the 50A outlet, to the panel in the trailer, you only have wiring to handle 30A, but it is protected at 50A. The only (and it is extremely remote) for you to have a problem with this, is if there was a fault on this run of 30A cabling.
2017 Escape 5.0 TA (someday soon, I hope
2015 Ford F150 Lariat 3.5L EcoBoost
2009 Escape 19 (previous)
“Most folks are about as happy as they make up their minds to be.” — Abraham Lincoln