The cover will snap on snugly (water tight seal). For the switch use a little hot glue to secure it as it's meant to be a lil loose. For the motor I would hot glue it down in the raised mount.

No need for supports as both should print fine (flip the cover upside down and the boat right-side up).

This is the electric kit I used if anyone is wondering... https://a.co/d/5zyHeln