You need to be careful loading up a battery like that.
The power output from the Amps is "continuous output" and in reality they will never be able to produce 1000watts.
Even at their RMS rating they will put a strain on a standard car battery, certainly in the winter when the demands from heated screen, lights, wipers, heater etc will be at the highest.
The ability of the alternator being able to replenish the battery is the main problem, even if the battery is in tip top condition, you cant take out more than you can put in and the starter motor will draw most of the power from a battery during starting.
You could fit the higher capacity battery from a diesel engined Clio.
Check the CCA rating, it should be 650 or more.