[ulbi1990]

pawn Код:

if(GetVehicleModel(GetVehicleTrailer(GetPlayerVehicleID(playerid))) == 584)

Checks in this case for the trailer ID 584. Than does it depends how you load the missions, if they have a clearly ID for the load (Box, Petro, Dirt) can you ask if the trailer id and the clearly setted ID.

Like this:

pawn Код:

if(GetVehicleModel(GetVehicleTrailer(GetPlayerVehicleID(playerid))) == 584 && ClealyID[Missions]==LoadID)