For anyone else coming across this thread some companies do pushchairs/buggies which are "fiat 500 approved" if they will fit in a 500 then they should fit in a Panda.
We got ours from Cossatto which while we don't have a fiat these days, we got a "500 approved" model which would fit in the boot of a convertible VW.
We got ours from Cossatto which while we don't have a fiat these days, we got a "500 approved" model which would fit in the boot of a convertible VW.