Flickering LEDs is usually attributed when hooked up to a car that has Canbus wiring for its lights, Its not a fault in the caravans lighting circuit, but to understand the problem you need to understand what canbus lighting is and how it works.
A car that has canbus lights (this can be LEDs or regular tungsten bulbs) rather than a continuous 12v feed to its bulbs instead its sends pulses of power through the wires, (basically switching the lights on/off/on/off/on/off etc) but it does it very quickly so to the naked eye it appears that the bulb is constantly on.
This method reduces the amount of current used and enables car manufacturers to use much thinner wires in production thus saving them lots of money, its very common on modern vehicles thesedays (even my 17 yr old bmw has canbus lighting)
So when wiring in the electrics for the towing socket a good canbus switching unit must be used to turn that pulsed voltage into a continuous 12v supply for the caravans lighting because even if you have a modern van with led lighting your cars circuitry wont necessarily be able to deal with those extra lights.
For what its worth, and given that you cant be expected to carry spare led lights units for your caravan when travelling abroad, LEDs dont fail anywhere near as much as regular bulbs, but you could carry some cheap battery powered bicycle lights that you could stick on the back just in case your tail lights should fail.