Well, as far as the thrust being limited because of the motor blocking part of the PVC pipe, that's really not a problem. Before I glued the motor pods to the PVC hull tube, I tested them out first... I taped the motor pods to a milk jug, put my electronics and batt inside, and gave it a run. The thrust is pretty amazing for a couple of little 140 motors! I meant to get a photo of this goofy "floating RC milk jug" test vehicle before I dismantled it, but I couldn't find my camera before I was ready to glue the motor pods to the PVC hull!

As far as being protected from plants and debris, I think this setup protects the prop pretty well compared to an open prop. I am concerned about something getting sucked in and clogging the area between the PVC motor tube and the motor, but I don't plan on running this in water that has much stuff to clog it up... haha... that's the plan, anyway... I guess I'll see when I really get it out in some ponds! Something like a leaf or piece of paper/plastic could possibly get sucked up, flat, against the intake and block the water flow, but hopefully some full reverse thrust will blow it clear!

A very experienced model sub builder in the RCGroups forum recommended using the bolt approached for the ESC connections, so I think I'll try that. I don't believe stainless steel bolts and solder would rust, but I will most likely cover the ends of the bolts, where the connections are made, with some silicone caulk. This will protect the metals from corrosion (if any), and provide electrical insulation, so I don't accidently short out my ESC outputs with a screwdriver or other conductive object. Instead of solder, I might just use some ring-tongue terminal connectors (basically a washer with an electrical crimp connection on it). I am a little concerned about soldering bolts that are screwed into PVC... I suspect that I might melt the PVC! I'll have to try it on a test piece of PVC tube before actually doing it on my sub hull!

Thanks for your comments and suggestions! Keep them coming!