There are two cargo liners. One is just for the rear space behind the 3rd seat, and there's also another one you can get that covers the whole area behind the 2nd seat. I don't remember where I ordered it from, I'll try to dig that info up tomorrow for you.
As for the NAV, I really doubt you can retrofit it in easily, there are whole different dash parts and such. Easier to get an aftermarket double din head unit that does nav I would think, but ask over in the NAV/Audio/Electronics forum and see if somebody has a better idea.
Welcome to the forum!
PS, all caps is normally considered yelling in internet etiquette speak, plus also it's much easier to read normal text than all caps. Thanks!