Our first trailer had the soft side type cover over the tanks. no cord etc. Lost it on the pull home from the dealer.
Current trailer has hard sided tank cover that is secured with a small bungee underneath. I notice it moves around a bit while towing. I would not tow it without the bungee in place. We often hit 30-40 mph winds while towing. That can be a combined effect of 80mph travelling over the cover.
2013 Coachmen Freedom Express 320BHDS pulled by a 2005 F250 King Ranch CC
A rainy day camping is better than a sunny day at work.