Truck Bed Speaker Wiring

So I got the idea of installing some bed speakers in the useless (IMO) open cubbies in my bed. I already have a 4X100 channel amp for my speakers in the cab. I am only in the brainstorming part of this project so any suggestions would be great. I am thinking of having a switch to either choose between my rear speakers and bed speakers, or having a switch to turn on bed speakers additionally with all 4 speakers. I thought if I used a switch to cut out the rears and send the signal to the bed speakers, I could send 100W and they would be much louder and sound better (also, not really concerned that the rears are off because no one would be in the truck).

Or, I splice into the rear speakers and put that on a switch, to be able to run all 6 speakers. My question is to anyone who knows more than I do, will this behave like I think and split the 100W between the speakers to 50W in the rear and 50W in the bed?

As far as speakers go, I would just find some marine grade speakers that would handle the power output, mount them to a sheet of metal,wood, or plastic, and simply screw it into the bed overlapping the hole from the cubby. I realize its not an ideal acoustic environment and I am not expecting extreme sound quality.

Also, I have a 6 blank switch panel that I would like to use one of the switch blanks for the bed speakers. I'm not very familiar with switches. Is anyone familiar with a rocker switch that isn't the usual on/off switch but can choose between 2 circuits?

 

Not sure I agree but many consider the rear door speakers to be a waste. One simple option would be to permanently disconnect the rear door speakers and connect that output to the the bed speakers. Could use the HU fader control (front/back) to switch between inside and outside.