This is a good idea of what your cage should come out looking like for your Enduro car. Although this pic shows 4 door bars, I would go with a min of 3. You want to make sure you keep the bar on the pass side low to the frame so that saftey crews have good access to you in case of a roll over.

You want to use the bar behind the driver to fasten your seat back and shoulder straps to. Try and build a support that you can attach to the rollcage to fasten your seat to. It's best if you don't fasten your race seat to the floor. During a rollover the thin metal of the floor may not hold your seat in place.

You should attach all your belts to the cage if possible. When buying a race seat you want it to be a snug fit. If you don't fit tightly in the seat, every time you enter a turn you will slide to the other side of your seat. After a few dozen laps this will get to be tiring and you won't be able to concentrate on your driving.