Never tried it but starbrite makes some products similar to damp rid.

http://www.starbrite.com/item/no-dam...idifier-copy-3
http://www.starbrite.com/item/no-damp-dehumidifier

can't you just take the canopy off and store it in a dry place.

Wish I could.unfortunately the very few places like that are either to far, or in questionable areas.The boat is stored next to my camper in a secure area,lots of friends to keep an eye on it.
The top although canvas,is really more of a permanent deal.It never comes down.The radar arch is permanent and makes the height on the trailer from ground to the top of the arch around 11 feet or more.

Dehumidifier
 

I am concerned about mildew in my Sceptre cabin that I am keeping in a boathouse lift above the water. I just bought one of these Starbrite buckets to put in the cabin. Does anybody have an opinion on these and their effectiveness? I would prefer to not have an electric dehumidifier if I can prevent it.