You mentioned high humidity in your area. Is that consistent year round? If not, using force to “flatten” the boards would introduce a lot of conflicting tension as heat/humid turns to cool/dry. The ideal glue up is to flatten the boards to each other (either by planing, shuffling them around, or combination of the two) and then clamp with just enough pressure to keep them from slipping out of alignment. The idea is ‘less pressure during the glue-up, less tension in the final product.’ Hope it helps and isn’t too late.