I use those desiccants (I'm assuming you mean those white crystal in tubs) and it helps with my boat. Not some much in cold weather as they are more designed to suck up water vapour.
Fitting one of those solar vents helped immensely plus I fitted more static vents in the hatchway.
I was thinking of trying one of those mains powered (I was going to say 240V but you guys are a bit poor on electricity over there lol.) Wardrobe heaters, they have a ceramic coil and are designed to left on for long periods providing a low heat.. In a closed up boat they would help a lot.
You could just leave the forward hatch slightly open to feed in an extension lead from your shore power.