There are a lot of variables that could be the culprit. Here is what I have surmised:
1. -10db is entirely too low for setting gains and is most likely contributing to over driving the amp. I use -3db test tones for setting gains. But it also depends on what quality media files you plan on using in the end. It was a little soft on music but would really sing on test tone burps at shows. Don't set the gain at the max volume on the headunit, instead use about 75-80% volume to keep the headunit from clipping. You can also use an oscope to see when clipping begins.
2. I would however look at the vehicle's electrical system too. Check for pinched wires, corroded connections and make sure grounds are solidly attached to clean metal. As others have suggested, try testing with a different amp as well.
3. What size alternator is in the car? Optima red tops are starting batterys not deep cycle and thus not intended for quick discharges from high current amplifiers. Starting batteries have very thin metal plates stacked inside, so when you constantly discharge and charge them you are generating heat, enough of which can warp and melt the internal plates of the battery leading to a shortened operating life and decreased overall performance. Deep cycle/car audio batteries are constructed differently to handle the abuse of constant charges and discharges. If you have a small alternator and no deep cycle battery then you are most likely experiencing voltage drop which isn't helping the situation and will cause trouble for your amp quicker.
4. Are the fuses blowing in the same location? Or is it a different location each time one blows?
5. Crossing the + and - wires as mentioned around page 5 could have caused damage to the amp, not enough to blow it right away but perhaps might be contributing to a slow death of components.
