I'm using this...

http://www.aipo.com.my/karakka.html

Comes with a rechargeable dehumidifier...

I buy a big digital display temp/RH from Jln Pasar as the small analog RH meter is very hard to see... see the link below as sample...
http://www.ebay.co.uk/itm/Digital-LCD-Temp...K-/310491447070

When RH is over the recommended level, take out a few hours to recharge la...

I'm also using the karraka dry box.  It comes with that electrical dehumidifier.  Charge it few hours til the beads turn from pink to blue. 

Basically the electrical dehumidifier is like this:  You charge it up for absorption.  Each charge is a one time absorption to bring the humidity down.  You have to experiment the level of charge to get the humidity level result to want.  To me I prefer to charge half way where the beads are light blue and not dark blue.  So when you put it in it dehumidifies the box close to 40%, while if it was dark blue it might bring it down close to 30% and sometimes under.