I’ve had generally good results with desiccants year round. I have both DampRid buckets and the renewable H2Out canisters distributed throughout the cabin and lockers.
In the summer when I’m on the boat, with no ac and no dehumidifier, the cabin tends to be wide open and very well ventilated with the companionway, two hatches and nine operable portlites. When away and the boat is closed up tight (There is still some air circulation through vents and hatch boat gaps.) the desiccant is very effective. I do always drain and dry the bilge and leave locker doors open when I close up the boat. Last year, I started leaving a small fan running when the boat is closed up. It may or may not have increased the moisture collected by the desiccant, but the cabin just seemed to smell fresher when I returned.
The only time I see any noticeable condensation in the summer is if the boat is wide open on an unusually hot humid day early in the season when the lake water is still cold. Then I’ll sometimes get some condensation in bilge and locker areas below the waterline. The upside is that the cabin feels a bit cooler then.
During winter storage, the desiccant does nothing in the cold dry winter months, but is very effective in the spring/fall temperature/humidity swings. After the shrink wrap goes on in the fall, I open the portlite in the head for some added air circulation. Also, everything is pulled out of lockers, lockers are left open and cushions stored on end for air circulation.