Build Your Own Remotely Operated Vehicle
This step is up to you.
Now that your three motors have a piece of PVC attached to them they can fit into your frame anywhere.
Build yourself a custom frame from your PVC pipe and position the motors to best improve mobility.
There are many different designs that will all have ups and downs, it is your job to find the perfect shape. It is easiest to use the two rear switches/motors for forward thrust, reverse and turning and use the third motor for lateral control.
Your ROV will undoubtedly have small leaks throughout the PVC and at the motors so attempting to make all the pipes airtight is tedious and pointless. Instead, drill a few holes in the PVC pipes.
This allows the water to fill the pipes quickly, evenly and completely. Then in order to make the ROV neutrally buoyant just add Styrofoam or sealed pipes with end caps on the top of the ROV with the zip ties. If you have the capabilities, knowledge and supplies you can customize your ROV with video cameras, lights, or even moving arms.
Have fun and enjoy your ROV!