i ran a 1000w rms amp with two subs, into my girlfriends 97 monte carlo. didnt want to drill so i went under the car and in the tailights.
But didnt upgrade anything, just put a 1 farad digital cap. and never had problems with battery or alternator. or dimming of the lights either.
although 1 farad prolly not big enough for 2100 rms.
