Just wanted to share. I never thought it's possible before.
Alpine mrp-f240 4 channel amp:

and 2 crossovers will fit great in place of Monsoon amp with more then enough airspace around for cooling. Will require some patience though.
I helped my friend to get rid of Monsoon amp in his firebird. We removed amp together with bracket, created bigger mounting bracket from plywood, using cardboard prototype to make a right shape. Bracket is secured nicely in one place by power antenna and crossovers and amp screwed to bracket. Amp and crossovers are not interfering with anything, including spare tire with this setup. We also run system pretty hard and amp temperature was absolutely normal. Very good SQ amp BTW.

 

good to know that the fit is there - I wouldn't exactly call it replacing though...might give people the wrong impression -- it's more "using a 4ch amp in the stock Monsoon location."

Many people that want to replace it would probably prefer 8 channels like the original (to call it replacing) -- the fronts are components so unless you have aftermarket fronts there would be problems because the woofer signal is full range while the tweeter signal is HPF (in the Camaro, the Monsoon amp does this).

You would have to lose the hatch speakers then (fine) but then if you wanted sail panel "subs" - 40wRMS is not enough power from this amp -- stock Monsoon supposedly puts out 300w peak for the sails, so probably between 55-75wRMS (anyone's guess) per sail panel speaker. This is also another filtered signal from the Monsoon amp.