Should be an awesome setup
Please report back with in use photos, and how putting them up and down works out.
It may be somewhat hard to push them under the boat. I tried a few different methods but settle on leaning against the outboard for stability, and using a paddle placed on the axle between the wheel and the leg, I could force them under the boat, but I had a completely different setup. Typically I would do this a hundred meters or so offshore, along with putting them up once launched since the prop could never touch them. Plus the tyres protected the outboard from hitting the bottom. Getting them up was a challenge too, but that paddle placed in front of the tyre towards the bow, could then be pryed against the transom and they would POP to the surface. Another way was to cut one loose, start the motor, turn hard the opposite direction to avoid a prop strike and gas the engine. With water pressure, the tyre would POP to the surface with a BIG SPLASH.
Oh just realized that Honwave design doesn't pivot. How the heck are you going install them on the water and remove them? I'd at least leash them. A pivot would make it easier to remove and install. Another modification?
As to the plastic plug I would get rid of it as it will hold salt water and moisture.