This is an update to last year's post on this topic. Played the same outdoor venue yesterday. Started at 7:00 AM with 100% humidity that eventually became outright rain. As before, the strings became very sticky to touch. With effort I was able to do slides. Was using GHS Pressurewound M7200-5 strings this year, as suggested by michael_t. Better than last year but still sticky.
Noticed the guitar player using a fingerboard spray. Perhaps GHS Fast Fret as suggested by trothwell. This is an easy thing to try, though I am not sure when another gig will occur under similar weather conditions. In the mean time I will ask him what spray he used and hot it changed the feel of his fretboard. If he found a spray unhelpful, then tapewound strings are an option.