Openhab thing/item for gas sensor

[seppi9]

Dear Forum
I would appreciate some pointers making a gas meter sensor working in openhab using a serial gateway. I used the water meter sketch and redefined S_WATER with S_GAS. The sensors shows up in openhab and reports data, but the data never gets stored as item.

The Sensor sketch uses:
#define CHILD_ID 1 // Id of the sensor child
MyMessage flowMsg(CHILD_ID,V_FLOW);
MyMessage volumeMsg(CHILD_ID,V_VOLUME);
MyMessage lastCounterMsg(CHILD_ID,V_VAR1);

things definition:
Bridge mysensors:bridge-eth:mybridge [ ipAddress="127.0.0.1", tcpPort=5003, sendDelay=100, networkSanCheckEnabled=true ] {
Thing gasMeter Meter_Gas [ nodeId=100, childId=1 ] {
Channels:
Type number : volume []
Type number : flow []
Type number : var1 []
}
}

items definition:
Number Gas_Flow "GasFlow" <flow> (Gas) ["Meter"] {channel="mysensors:gasMeter:mybridge:Meter_Gas:flow"}
Number Gas_Volume "GasVol" <volume> (Gas) ["Meter"] {channel="mysensors:gasMeter:mybridge:Meter_Gas:vol"

openhab receives the messages and shows them in the gateway debug output:
Message from gateway received: 100;1;1;0;24;36
Node 100 found in gateway
Child 1 found in node 100
Message from gateway received: 100;1;1;0;35;0.360
Node 100 found in gateway
Child 1 found in node 100

But the output of the other (working) sensors is then processed and stored:
Updating channel: hum(V_HUM) value to: 49.2
Humidity1 changed from 48.2 to 49.2

How can I specifythe channels correctly in the things and items file? Would it be better to use seperate child Ids instead of channels?

[seppi9]

just a small correction: it's a Raspberry Pi Gateway, but probably this makes no difference