to add, if you keep the jack in its oem place, if it's like mine, in the pocket behind the folding seat, you'd want to make sure you can get to it, or, move it to the tool box.
I've found the Kobalt tool box it came with highly useful and I don't worry so much about behind the seats. Also, if yours is like mine, you may have a pull-out cargo cover so you could hide things.
My main concern at the time was making a flat platform for the dog, along with storage, and something like CrabGuy's works really nice for that. But the dog doesn't care, and, I don't use the '99 much now, it's sorted, I should sell it, I just make sure I exercise it often, otherwise I'm mostly in the '97 because it has more creature comforts.
Admittedly the tool box does shorten the bed - it has about 5" under it, which isn't highly useful except it lets you get long things in, depending what it is. But you can take the box out for special purposes, I haven't, but it doesn't look like it would be very hard.
One of the huge issues (to me) about the '99 is, like you see there, the jack mounts to the rear while on yours, again if it's like mine, it should be just smooth there. Technically for the later ones you should be able to get a smooth panel to fit in the middle but I don't see them much (means jack was mounted elsewhere). CrabGuy has the jack etc mounted inside this box, there's still plenty of room left.