Amp Recommendation/Tweet Location/Sub Placement

[SeriousBlack]

Hey all - first post. Just got my black 5 dr Yaris RS and am planning my audio upgrade. I'll be getting my MB Quart QSD 216's next week for the front. For the time being, I'm leaving the rear speakers but will eventually get some decent quality coaxials. Recommendations on those?

I've been reviewing the tweeter location threads to get some ideas. Any consensus as to optimal location bearing in mind sound quality, environmental (heat/possible rain water) and security issues?

I have a JBL GTO 1200 sub from my previous car as well as a GTO series mono amp. That'll be it for the rear. Thinking of doing a custom MDF deck install w/o the spare tire. It's not my first choice on a sub but I don't want to shell extra coin to replace what's been a solid sub. Any suggestions on installing the MDF deck would be great. I'm particularly concerned about placement of my mono and new (see below) amp. If I placed them on the UNDERside of the rear deck, will I have overheating issues? I'm more concerned about security than show/display.

Finally, given the above install and the fact I'll be keeping the stock head unit, any recommendations on a quality amp to run my QSD's from? I'd like to stay in the $200-300 CAD range for the amp.

Cheers everyone.