Bed bugs

So here I am, enjoying Girls' Weekend with my in-laws in lovely Geneva. There are few requirements for girls' weekend, though there is generally always fondue, shopping, a trip to an old house and/or museum, and getting lost. 
Today, after shopping but before getting lost and eating fondue, we visited an old house - Hubbard House, an underground railroad museum in Ashtabula. It was one of those small-town museums in which local history buffs have taken a house of some historical significance, crammed it full of as much period paraphernalia as they could find, and hired docents to tell vague stories and spew false etymologies. 
The false etymology - or alleged false etymology - in question was the origin for the expression sleep tight. According to the folks at the museum, the expression sleep tight stems from a time when bed frames held up mattresses using a web of ropes which had to be tightened regularly to prevent sag. This makes sense on its face - mattresses were held up with ropes, and those ropes did need to be tightened - there were special wooden fork things made just for that job.
But I smelled shenanigans. For one thing, I have a hard time imagining people warmly reminding each other to engage in mundane daily tasks as a way of bidding someone goodnight. Wouldn't it be sort of like saying "Good night, go change into pjs and put some sheets on yourself." But people say stranger things, so I did some homework.
Phrases.org was one of the many sources that reinforced my skepticism. It says that the phrase didn't appear in print until the mid- to late-19th century, and became most popular in the mid to late 20th century, long after the whole rope bed thing went out the window. There's also the inconvenient fact that, according to all the sources, there's just no evidence to support the idea. It's an interesting hypothesis, but there's no linguistic evidence - no references to a literal origin in literature or non-fiction. 
Further, there's evidence to the contrary. According to The Word Detective, the word tight was commonly used in the 18th and 19th centuries to mean soundly or thoroughly. Occam's razor - the disappointingly dull etymology is probably the right one. Okay, that's not the precise definition of Occam's razor...
 Word Detective Evan Morris agrees with my opinion of docents, by the way. He says "frankly, I have heard so many utterly absurd word and phrase origins attributed to tour guides that I have been forced to conclude that they constitute one of today's major "vectors" or carriers of unfounded etymological "urban legends." I know it must be difficult to maintain an interesting line of patter all day long, but there's still no excuse for inventing little linguistic fables out of thin air. Caveat viator -- let the tourist beware."