Still though, custom textures that the .esp is solely dependant on? Is this easy to import? Pretty sure earlier today ethatron confirmed that the .esm land textures seem to have no brown-texture problem as shown by an LOD mod for Skyrim itself -
OT: It's not that, because: http://skyrim.nexusmods.com/downloads/file.php?id=4834 , it's something else.
Which implies pretty strongly that dependent .esp files which don't link directly to the textures.bsa themselves are the issue. Importing custom textures I'm assuming would be directly referencing them, (unless oscape requires they are also in a .bsa.. possibly). You can't save over the .esm so any links to external textures would have to be native to the .esp - well it's worth a try. Any tutorials kicking about on adding custom textures?
EDIT - also, seem to have some half-OK results from a variety of stuff now -
http://imageshack.us/photo/my-images/819/screenshot10ej.jpg/
http://imageshack.us/photo/my-images/88/screenshot11sz.jpg/
That's using the CK to generate just meshes and LOD water (fairly quick at high priority, about 3 minutes for a 88x84 worldspace), then using the Skyrim beta of TES4qLOD to generate high quality 4096x4096/quad distant textures. Finally used Oscape to generate normal maps and chucked em in the same folder.
Not perfect, but then neither was my texture-painting skills in the CK - I just splashed a load of pretty contrasting textures everywhere so that blocky effect may be partly down to my lack of artistic skill and partly down to a lack of textures diffusing for some reason (a limitation of TES4QLOD I'm guessing from the readme that came with it). On the plus side a bit of clutter might tidy it up for the time being and at least it's not entirely brown yet got rid of the gridlines/huge black sections (those black sections you may see on those shots are actually representing a dark texture I painted on).