Hi
I have some questions:
1.- xml-rpc is going to be through https or http?
If https it could be a little bit problematic with the esp8266 module, maybe the latest firmware support it, but the programming will need to be done using the SDK not the arduino IDE.
Of course is preferable the https instead of http for more security
2.- Configuration? It need something called captive portal or if you don’t want that it can be done using the serial port, in order the get and set configurations.
3.- Duration of the battery?
4.- If cannot connect to the network, What action will take? Store in memory until it can connect and send the data.
5.- As this are small devices. Have you take into account another communication methods? There are some other communications protocols that support encryption. I can suggest MQTT, but it need a broker.
Think in this scenario
1.- In the first configuration the user just set in the ip of the broker and the user/password.
2.- The ERP will be another MQTT client that will create a new entry in the ERP using xml-rpc each time a new device is connected.
3.- The erp will have a list of devices and their status: like connected, disconnected, attached in the car, available or other status that you think.
4.- When a new car enter, the ERP user will turn on a device, and this device will appear in the ERP as a available and the ERP user will select and fill the with the data and push the button configure device and it will be configured according.