We had a landrover written off due to this a while back. I have also had a very near miss myself with the same trailer (snaking across all 3 lanes of the M8). Luckily there was a gap in the traffic.
I have been towing heavy trailers for 20+ years with a variety of vehicles, so here's my tuppence worth.
Snaking is caused by the drivers response to a small movement which, if timed correctly (or incorrectly depending on how you look at it) exacerbates the yaw. So you feel a small wag and unconsciously apply opposite steering pressure at the exact moment that the trailer is moving back in the same way. This makes the yaw bigger not smaller. The thing to do is learn to not react to the initial wag. Just hold your line.
Accelerating out of a snake is best avoided. It doesn't always work and if it doesn't work you are going faster than you otherwise would have been so the resulting accident will be worse.
Best policy in my experience is to lift off the gas and don't brake. Try, if there is room, to make a slow turn, change lanes on the motorway for example. Don't try and make corrections to the steering, try and hold your line or your turn if you have room to make one.
The best policy overall is prevention.
Do not have any tail weight, you need positive pressure on the drawbar at all times.
Do not however have too much nose weight as in the picture earlier in the thread this lifts the front wheels and severely reduces braking performance. I discovered this to my cost when I went up the back of a lorry on a wet road towing a tractor on an ifor.
Use a trailer with indespension type axles rather than leaf springs, these are much better in my experience.
Make sure the towing vehicle is up to spec. Our defender that rolled had no anti roll bar on the rear axle, (many don't) our other one does. There is a noticeable difference in towing performance between the two.
Make sure your tyre pressures are correct, soft tyres help exacerbate the yaw, especially on trailers with high walled tyres, sot so much of a problem on the modern low profile jobs.
Finally, test your load, I always do this. Once loaded you set off and at a moderate speed, 30-40 mph, on a quiet straight bit of road give the steering a wee jerk. This will make the trailer wag, then hold your line and watch it in the mirror. If it comes back into line immediately then all's well. If it keeps wagging for any length of time then stop and adjust your load, if you can't adjust it then you will need to drive accordingly, i.e. slowly!