I'm trying to remember the name of a movie from the 1970s in which a father creates this really cool house/pod with gadgets that an entire family can live in, and then convinces his own family to try it. The teenagers arrive, guitars and all, and befriend a seal. They start to enjoy the place until the mom accidentally releases the garbage without first sealing it. Sharks come... but not too scary and of course they all get rescued. It's a great kids film... just can't remember the name! Thank you.

This was just answered over at imdb.com. It's Hello Down There from 1969, which evidently was a significantly dumb movie and yet it featured an impressive cast, with Tony Randall, Janet Leigh, Jim Backus, Ken Berry, Roddy McDowall, Charlotte Rae, and Richard Dreyfuss.