I'm not feeling confident about the 'boat' part of all of this. First, what kind of boat would one propose was used? ie many boats, like say a smaller fishing type of boat, are not high enough to keep things hidden well enough, ie if someone happened, along a long shoreline(?) to be looking out with their binoculars (which presumably every resident living on the water might own), they might see something worthy of noticing/reporting.
Secondly, if a larger type of boat, or even if a smaller type of boat, it is a fact that noise carries on the water.. voices can be heard, boat motors can be heard.. would none of the full-time residents have heard a boat? Like others have mentioned, this time of year isn't exactly boat season yet. Wouldn't someone have noticed the sounds of someone on the water, especially if very late at night?
Third.. I can't see any type of operation taking place IN the boat itself, other than possibly the transportation of the body for dumping. I'm thinking it would have to be one LARGE boat to have performed much else on there, due to space constraints, noise considerations, and balancing issues.
Maybe I am envisioning things wrong, just due to my own personal experiences with smaller types of boats, and having lived on the water every summer for much of my life.. but I'm just not feeling it about the boat involvement. Isn't there anywhere on the lake where a body could be 'driven' to by road, and dumped from a bridge, or a bank? I'm not understanding why people believe that where the body was discovered, was the same place the body was dumped?