How about the summer in a colder climate like Alaska? Beautiful mountains and lakes and possibly warm enough during the day for revealing clothing. I have been told that there is a bug/mosquito problem in Alaska in the summer (at least in some areas) so that challenge will remain. If not warm enough, the reward challenges can take them to a hot springs or spa so that people can get nekkid. Or we can have 'strip immunity challenges.'
Personally I feel that a hot guy/girl will still be attractive in warm clothing, maybe more so. As the show gets to the end, the contestants are often too skinny, scarred, or bug-bitten to be attractive (except for Jamie and BobbyJohn...the only people to look better in the jungle than in real life!). Let 'em wear clothes and give us some new environments!
If we insist on warm climates, maybe the Sonoran Desert and for rewards they can come to Vegas or Phoenix or Palm Springs. Or the Sahara Desert. Or the Sinai Peninsula. Or the Mediterrean coast of Greece or Turkey. I think it is time for some fresh ideas because palm trees and islands have become tired.