The front seats don't recline flat, and even fully reclined doesn't help much. You'd have to place a long item on top of the reclined passenger seat headrest which is pretty high off the floor. In many cases, more space would be available by sliding the passenger seat fully forward and tilting the seat back toward the front of the car. The seat back won't remain tilted on its own, so something would have to be pressing on the seat back to keep it tilted forward.
Long, narrow items could fit between the front seats. The center display prevents long items from being placed on top of the dashboard.
An i3 can be driven with the rear hatch partially or fully open. Doing so automatically activates brake, running, and turn lights in the bumper so that lighting could still be seen by following vehicles. Unless the REx engine is running, no nasty exhaust fumes would be sucked into an open hatch while driving. I would tie the hatch down to prevent it from opening fully. I don't know how well the hydraulic struts that push the hatch open would deal with the weight of the hatch over many hours of driving.
Secure any items being carried so that they don't impale you during an emergency stop or a front collision.
