[TowerTalk] guage of wire for 500 watt antenna?

[Gary Slagel]

I'm hoping to get to Belize to work ARRL DX CW contest this year and I'd like to take my Elecraft KPA500/KAT500 and operate 500 watts. I will be at a friends house and not next to the ocean so I'm thinking of getting a doublet up in the air as far as I can on a fiberglass pole, feeding with 450 ohm ribbon and tuning it on 10 thru 40 and maybe 80M. 
The fiberglass pole won't take too much weight so I'd like to go as small as I can on the wire.   Any suggestions or input?
Thanks, Gary KT0A