A trailer is a great alternative to panniers because there is no tedious mounting involved. During my recent expeditions, I used two trailers: BOB YAK and Extrawheel.
Both are recommendable for long expeditions, but I prefer Extrawheel for the following reasons:

-	twice cheaper than BOB YAK,

-	weighs less with the same load capacity (4.8 kg vs. BOB YAK's 6 kg),

-	because of big wheels, Extrawheel has got lower rolling resistance,

-	the mounting system automatically uncouples the trailer in emergency, and prevents the hanger from bending under heavy loads. This solution is simple and effective, involving no screws or plugs that can be easily lost,

-	carrying strap,

-	in case of a breakdown, all spare parts – from the tube to the hub, are standard and easily available,

-	designed and manufactured in Poland

Trailers have some good and bad points:
Advantages:

-	with less load on the rear wheel, you can use ultra light tubes and tyres,

-	very low centre of gravity,

-	low air resistance,

-	easy mounting,

-	possibility of using bikes with rear shock absorbers,

-	the BOB YAK trailer also serves as a kick stand – you do not have to lean the bike against anything,

Disadvantages:

-	trailers weigh much more than racks (Extrawheel Classic weighing 4.8 kg, and BOB YAK just above 6 kg, but the newest Extrawheel Voyager only 3,9 kg). However, the difference is not that pronounced, when we realise that panniers are usually replaced with lighter sacks and bags,

-	when the BOB YAK trailer is heavily loaded, make sure that the rear derailleur hanger does not get bent, because the trailer is rigidly attached to the bike,

I am an avid supporter of a trailer because you do not have any rack-related problems and once you unhitch a trailer, you can immediately hit the mountain roads.