Alternate use for Simms Dry Creek Chest Pack
I agree that most chest packs are too bulky for double-handed casting.
I have the Dry Creek chest pack, but frequently thread my wader belt through the belt loops on back and wear it on my left hip, kinda like a holster for my gear. Casual dunkings are OK, but the zippered openings do not close completely and will leak if constantly submerged.
The problem I have found with all these waterproof packs is that the water-resistent zippers are more difficult to open and close with one hand, and they yank on the belt/harness as well. Not to mention the two handed process of rolling closed the lumbar pack. Which can make it a PITA having to dig your essentials out of the pack every 5 minutes. To solve this problem, I have a neck lanyard that holds my basic tools, tippet, and a small foam flybox / or SA System-X Nymph/Dry flybox, so I only need to get in the pack for "major overhauls". (I like the the SA box a lot. It is cheap, light, waterproof, and has two compartments for shot & indicators(heresy) or whatever) I usually stuff the flybox/free hanging end of the lanyard down the front of my waders to keep it out of the way while fishing. In the winter or when raining, I clip the lanyard to the D-ring on the front of my jacket to keep it from swingin' around.
I also have the roll top pack (which I use more for wet wading/swim-fishing in the summer with my 3-5wt single hand rods). It is completely waterproof in the main compartment, but the zippered pocket still leaks a little. The lumbar pack will muck with your bouyancy if you go swimming, making your ass float and trying to push your face in the water so I wear it in the front and float downstream on my back from spot to spot when neccessary.
As for access to the stuff in the packs. The roll top lumbar pack usually has to be unbuckled to swing it around front, so it can be a pain holding your rod AND using both hands to fasten the buckle. There are two small zippered pockets on the "wings" of the belt/pack that are not waterproof, but very usefull and easy to get into with one hand.
The chest pack is narrower and slides easily from a position over my left rear jeans pocket, around to the front, and back again, for unhindered casting and stripping. You can also position the double zippers on the side of the pack as opposed to the top, allowing you to reach into the side during a downpoor and get minimal water inside.
Since getting these packs, I haven't fished a single day in a vest!