I have managed to bend 5mm ply to accommodate the slight radius of a fore deck, but that is with a good support structure strong glue and stronger clamps, my cabin roofs are curved, but from 1.6mm ply, so you could do two layers (I find one layer curved is plenty strong) I have curved 0.8mm ply very slightly in two planes, but it constantly wants to spring back (once again cabin roof with very slight fore and aft cure as well as side to side).
Ply will naturally curve more one way than the other, so use this to your advantage when deciding on which way you will cut out of the ply.