[LarzI]

You could make a custom function

pawn Код:

stock SetVehicleAndTrailerPos(vehicleid, trailerid, Float:posx, Float:posy, Float:posz)
{
    new Float:bx, Float:by;
    GetVehicleTrailer( vehicleid );
    SetVehiclePos( vehicleid, posx, posy, posz );
    GetXYBehindVehicle( vehicleid, bx, by, 5.0 );
    SetVehiclePos( trailerid, bx, by, posz );
    AttachTrailerToVehicle( trailerid, vehicleid );
    return true;
}

pawn Код:

stock GetXYBehindOfVehicle(vehicleid, &Float:x, &Float:y, Float:distance)
{
    new
        Float:a;
    GetVehiclePos( vehicleid, x, y, a );
    GetVehicleZAngle( vehicleid, a );
    x += ( distance * floatsin( -a+180, degrees ));
    y += ( distance * floatcos( -a+180, degrees ));
}

Can't garantuee that it will work 100%, or work at all.