I was thinking about this the other day. There are two ways to steal a bike, "ride away" and "haul away". When you have your bike loaded up it's pretty darn heavy and if you have a trailer it's impossible for one person to lift without disconnecting so you eliminate a lot of "lone outlaws". If you take a cheap cable lock and tie the bike to something you will eliminate 99% of the opportunistic thieves taking the bike away in a pickup truck or something. Cutting a cable takes time. If you take a strong "Master lock" (the type used on gates and lockers) and just put it through the chain ring you'll eliminate all the "ride away" threats short of those with monster bolt cutters in which case NO lock will save ya.
So, on a long tour, I'd take a lightweight combination cable lock (so you don't lose the key) and a strong ordinary lock instead of a big heavy cable. You'll eliminate so many of the possible scenarios for theft that the remaining chances of theft are minuscule. Stopping theft from your packs is the biggest risk you'll have remaining.