Gunnera is not going to grow in Zone 10. I wish it would, but it's just too hot here in the summer for it. Here's some growing in Scotland - Zone 7 (due to the Jet Stream, the country has some weird climate zones.) That's a full size bench in the photo - 8' long.

Hi
would agree with fawnridge . Slow painful death in florida lol They are from the tropics but high altitude so much cooler . tried a couple of times myself
if you want gigantic leaves some of the aroids or water banana much better choices .. Mabe some aquatic palms??
gary