Would the 1215 ATM not include the awning? I thought the 300kgs was for the awning battery etc ??
The 300 kg difference between the TARE and the ATM is sometimes referred to as the 'personal allowance'. This means that you have 300 kg for water, gas in the gas bottle, clothes, food, utensils etc. That 300 kg disapears quickly! The water tank and filling the gas bottle alone is almost 100 kg.
If you get the battery and awning factory fitted, they include it in the TARE, so the TARE will increase by roughly 45 kg just for those 2. The ATM will also then increase by 45 kg. If the awning and battery are fitted after the camper is built (not factory fitted) then this weight generally falls within the personal allowance, so the TARE and ATM don't incease - it just means less can be loaded into the camper.
Either way, you will have to travel very light to get within the 1200 kg limit.
Jayco just released a lighter weight camper trailer this week - not sure what its called but it might be worth a look-in!