The alien spaceship is a dressed-up version of the diving bell from another Irwin Allen series, Voyage to the Bottom of the Sea (1964)
Dr. Smith sure was lucky that the Robinson family thought to pack a wheelchair for the journey to Alpha Centauri.
The Fish-Man is borrowed from Voyage To The Bottom Of The Sea TV series. Season 2 episode 24 titled "The Menfish".
The cosmic radiation meter seen at about 33 minutes in is actually a dwell tachometer of the type used by auto repair shops.
The top part of the unit next to the alien space ship is the same prop used for the Robinson's water distillation unit.