Why is all of my inside floors and under the seat constantly having water held.

My guess is you have the power sunroof, which has 4 somewhat hidden drains. The tubing tends to shrink away from the fittings, then leaks like a sieve inside the car. You can order new ones from any GM dealer. Instructions can be found on-line to replace them. Not too difficult, but the headliner had to be pulled away near the windows and the plastic pillar covers removed as well.