Last show of the series.
A book on "Alias Smith and Jones" puts this show's filming schedule at an incredible 22 days - nearly four times as long as Universal normally allotted to a one-hour series episode. It appears that director Alexander Singer filmed this entirely on the sets of other episodes, getting two or three minutes worth of film in a couple hours per day, after the "main" episode had wrapped its day's work.
A second look at the production schedule shows that this show went into production two days after the season opener "The Long Chase," and filmed alongside it in Utah for eight days before coming back to Hollywood in late July 1972, where it was again filmed alongside "The Long Chase" for the studio scenes. This must have been rather interesting, since the shows had two different directors - did Jeffrey Hayden go to Utah with the "Only Three to a Bed" script with his hand and pick up whenever Alexander Singer finished his work on "The Long Chase," and repeat the procedure at the studio?
The episode title (taken from a sign on a boardinghouse where most of the male characters bunk) is a bit of an inside joke. Nobody actually sleeps three to a bed since one of the three is always on watch, and one character adamantly sleeps by himself because of his Puritan beliefs (which play a role in the story development).