I had a quick look at these dry suits you mentioned (expensive!)... They certainly look as though they'd keep you warm and dry, but I'm fairly sure there is a major drawback in using one for the purposes you have in mind, unfortunately. Basically, mud is denser than the human body and the laws of physics mitigate against sinking below waist/chest depth in mud because of the floating point that is reached when immersing an object in a semi-liquid, gelatinous substance. This doesn't apply when the substance reaches a certain thickness, but that causes another problem since the layer 5 ft below the surface becomes more difficult to displace and cannot easily travel outwards and upwards in order to make room for the object taking it's place. Being on the skinny side is definitely an advantage in that respect, but this only helps so much.
Pete bogs have a naturally far lower density per cubic foot than clay pits for example, which is why pete is better type of mud for sinking very deep; as demonstrated in this short video
http://www.youtube.com/watch?v=SylEMyamVwc Theoretically, gelatinous clay could be aerosolized by introducing millions of tiny air bubbles whilst pumping it through a pipe in gelatiouns form and at high pressure, then allowing it to dry in situ. I know that specialized industrial equipment can do that, by it's a pretty elaborate workaround. You know how a Wispa bar is lighter than it should be? Yeah, like that.
As far as I can tell, a dry suit would substantially increase you buoyancy / volume-to-weight ratio and raise your floating point higher than it would otherwise be. On that basis, a contour-hugging wetsuit would be more suitable if you want to go in really deep and possibly submerge. That is all theoretical speculation, though - with your real world experience of wetsuits and dry suits, what do you think about this?
Physics is a bitch.
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