Dude, wherever you put your speakers, they'll sound best if they have a direct "line of sight" to your ears. I wouldn't go sticken' em down near your feet unless they're only for "thinking music"

Bass is omni directional, that means it goes in all directions. Trebble on the other hand only travels in a staight line from the speaker, if you can't see it, you are only hearing reflections.

I suggest you cut holes in your doors with a jigsaw or put em in the rear shelf.

speakers mounted in the footwell area can be sitting higher than if in the door panel, the speaker mounts are angled as much as practicle so that the cones are facing into the cabin(towards the driver/passengers).
the next option for this sort of setup is to run splits with the midrange in the door or footwell and tweeters mounted on the dash or screwed to the A pillar.

unless you plan on cutting holes in your doors up near the window winder or higher there'll be no advantage unless you have ears in your knees ??

as for the fiberglassing, it's simple to make these types of pods. if you're interested in having a go pm me and i can email or post up a couple more pics. all up these cost me around $20 australian to make and a few hours on each

This is possibly common knowledge, and I don't know 72 coups very well but it's worth a mention. I once saw a guy put tweeters in his dashboard air vents. You couldn't see em but you sure could hear em!