Don't worry too much about the trigger locks, here are the reasons:
We have several Portuguese shooters travelling around air rifles (including Lisbon airport) without a trigger locks, air in the rifle, etc.... No issue till now.
We are going to have a meeting with the police in the 1st quarter of 2016.
The idea is to eliminate any possible stress that we don't expect to have at all.
According to the Portuguese Law fire arms need to travel with a trigger lock or mechanism that would prohibit their use , etc... (read law below)
Since there's no law for air rifles, to prevent any issues everybody follows the fire arms law. For example using the trigger lock.
If we read the law carefully it says "... other mechanism or part without whose lack would prohibit shooting ..." in our case it can be for example removing the air from the air rifle.
SECTION II Use of firearms, power and defense aerosols
Use, possession and transportation
A. Firearms must be transported in bag or case appropriate to that type, with an appropriate security conditions, separately from the ammunition, with trigger lock or mechanism that would prohibit their use, or part without whose lack would prohibit shooting, which must be transported separately. (....)
If you have any question let me know.