[Sergei]

Each trailer is separated vehicle basically, but it is automaticly spawned and attached when you spawn train.

And for examples about variables.
Make an array for those special IDs you need like:

pawn Code:

new VehID[XXX];

And when you spawn those vehicles which you need IDs for later you do like:

pawn Code:

VehID[X] = CreateVehicle(...
or
VehID[X] = AddStaticVehicle(...
or
VehID[X] = AddStaticVehicleEx(...

And later on in your script you just use VehID[X] instead of actual IDs.

Of course XXX are just symbols in this example, you need ot change them with actual values.