No problems here with 155x100x35 , 4mm walls, 4-lower 4-upper, solid infill hollow-box w/ lid. (that's a 60mm fan snap-fitted into a 5mm recess if it helps with context, and an awful awful lot of molten plastic during prints of the first 10 layers
)
The one next to it is 120x95x35, 4mm walls, 4-lower 4-upper, solid infill hollow-box w/lid - snap-fit that snaps and fits.
I'd offer up copious other examples, but those two happen to be on my desk right now.

Both of these have been printed 'unenclosed' with no love or attention given other than selecting the correct filament type for the filament at the time, and hitting 'print'. If I had cared, i'd have set z-height a bit better to get a nicer surface finish on the lid, and then I wouldn't have pointed a heat gun when doing some heat-shrink at the lid of the box on the right (which is whats caused the feint deformation on top) - But I wasn't printing these other than to be functional, and I still got what is in the pic. Mark - you got any idea what I'm doing wrong either ? 
If I had to make one general observation about those dealing with "problems" generally on the forum it would be (directed at no specific individual or otherwise so don't bother with a flame war) - stop over thinking it. A fair amount of hand wringing around here is spent dealing with perceived problems/problem source vs actual problems/problem source and their established solutions (and yup, cherry picking from that list of fixes when a genuine problem is identified isn't applying the fix... its over-thinking it again by assuming there is a shortcut to be had ).
Either way, isn't the inherint joy of 3D printing learning wonderful new stuff? If you wanted instant satisfaction (with caveats
) with ignorance to the process theres always shapeways 