Another item some of the guys use when wreck diving is a OMS tube canister for the PLB. Just clip it on you and go, good to 660 feet so I think you won't have to worry about it getting wet.

http://www.omsdive.com/microfix.html



PLB-CAN-K 660’ Depth Rated Canister, slightly larger than the BCA298 to house the ACR Microfix PLB 9.19" OAL 2.5" ID 2.88" OD Buoyancy w/ PLB +0.15 lbs

http://www.omsdive.com/bc_access.html



Another option
I've been using a Nuuk for my GPS and Steripen and batteries, I don't know if it will fit the PLB, haven't tried it but I bet it will. This is my most used watershed bag and is good to 300 foot underwater at a price if $65.00 with a lifetime warranty and no O-rings or maintenance to do of the bag.

http://drybags.com/home.html