I was wondering about the cable length as well, but some of the Waeco circuitry has a "gotcha" in it anyway (model dependent, you'll eventually find out).
We had a Waeco CR140 front-opening fridge in our previous caravan. It typically drew 5.5A when cycling, 6.5 when working hard but was rated to draw 7A. This would regularly kill our battery overnight until I found out why.
The electrical length of cable in our van was something like 5m which for just a short way across the van didn't seem like much but in 12V applications it makes the world of difference. The thinner 6mm cable used was the problem - despite 6mm being the recommended cable for the amount of power being used.
What was happening to us was this: as the sun went down, the solar panels stopped charging the battery. The fridge would start the compressor and the voltage would fall to around 11.9-12V. This was fine to start with. Each subsequent start of the compressor would see the voltage drop a little more (as you'd expect).
By midnight, however, the battery voltage dropped enough so that the voltage presented on the other end of this cable fell below the Waeco circuit's battery protection cutoff voltage. The compressor dutifully stopped, the voltage returned and 30 seconds later the compressor started again. This killed the battery.
Why did that happen? When you place a load on piece of wire, it will present a different voltage on each end due to the amount of the load, the thickness of the cable and the length of the cable. The thinner the cable, the more the drop. The heavier the load, the more the drop. If you have an unloaded cable (just connect a small lead to a battery) and measure both ends you'll see similar voltages on both ends. Run a 5A device with that cable and measure it again - you'll see a difference.
So, knowing that - you may be able to resolve your problem much more satisfactorily. Replace the cable with at least 8G cable, available from Jaycar in a figure 8 (click
here for the stuff that I've been buying). For lengths up to about 8m this is going to be enough.
That may not resolve your issue though. It's always good to have heavier cable regardless - you whack in a fuse to protect it anyway, but the heavier cable has less losses and therefore is more efficient. The Waeco circuitry may have a problem of its own. Some models had a polyfuse that was faulty - the fuse itself caused such a large voltage drop across it that the circuit on the other side decided the battery was too low. If you replace your cable, or even easier just use a short (good) cable to test it and still have the cut-out happening, you should be able to get it fixed by Waeco.
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