Hi Jeroen,My 100HP had Isofix and IIRC i's a bar behind the (split folding in the 100HP)rearseats. Bolted onto the chassis ob the same place the seats and/or belts are bolted.
Shouldn't be that difficult.
gr J
100% sure I had Isofix in the Panda as well as now in the 500 Abarth.