I agree. This is an ongoing subject with caravaners, a tracking device. From reading many articles and forums regarding getting a tracker, the general consensus seems to be "Don't bother". As you point out, they're expensive and the savings on insurance just isn't worth it. They're also not infallible. Several members have still lost their caravan despite having a tracker. And at least one member I know eventually had their caravan returned, wrecked! They said they'd rather not have seen it again and just got a new one from insurance. Instead, the insurance paid out for the repairs to the damage!
So yes, forget trackers. If a thief wants your caravan, no matter what security devices you use, they will have it. And bye bye caravan, thank you for the new one! ;-)