I'm curious to hear more about this frame flex. I can't find any old posts about it. I can't imagine there being much flex at all or interior "stuff" would start breaking and not lining up.
My TT is 9 years old and the previous owner said he averaged 11,000 miles a year with it, but everything inside is still tight as a drum. I would think if the frame flexed much at all, it wouldn't take too many chug holes for interior components to begin showing signs that theres been movement.
I know theres gotta be SOME, but personally I doubt theres enough to establish concerns about the slideout for this debate.
I'm sure it varies by model as well.