I agree on the bal leveler; great for leveling side-to-side and the bunk end covers; great for hot areas with direct sunlight. And under pine trees the take the bird dung and sap and easy to clean.
If connecting to power pedestals, I recommend a power power management system such as from Progressive industries. A surge protector only protects against a surge; whereas a power management system protects for low voltage (believe it cuts off everything under 105 volts).
And if for piece of mind while towing; tire pressure/temp monitors such as from TST or other companies allow you to keep an eye on those trailer tire pressures and internal air temps.