Something like that maybe... but it's hard to know, it's kind of approximate.
pawn Code:
stock GetXYBehindVehicle(vehicleid, &Float:x2, &Float:y2, Float:distance)
{
new Float:a;
GetVehiclePos(vehicleid, x2, y2, a);
GetVehicleZAngle(vehicleid, a);
x2 += (distance * floatsin(-a+180, degrees));
y2 += (distance * floatcos(-a+180, degrees));
}
stock GetTrunkPos(vehicleid, &Float: x3, &Float:y3, &Float:z3)
{
new Float: x, Float: y;
new Float: sizeX, Float: sizeY, Float:sizeZ[2];
GetVehicleModelInfo(GetVehicleModel(vehicleid), VEHICLE_MODEL_INFO_SIZE, sizeX, sizeY, sizeZ[0]);
GetXYBehindVehicle(vehicleid, x, y, sizeY/2);
x3 = x;
y3 = y;
GetVehicleModelInfo(GetVehicleModel(vehicleid), VEHICLE_MODEL_INFO_REAR_BUMPER_Z , sizeX, sizeY, sizeZ[1]);
z3 = (sizeZ[1] + sizeZ[0]/2);
}