Tell me where the structural integrity is-

[JD33]

Dan, I don't think that you are far off on your guess re fuel mileage LX vs M380. Personally I can only speak of an LX, and I am very happy with the power to weight ratio and fuel economy of the coach. Pre 2004 for sure there is no emissions concerns, my 2001 LX does not even have an EGR. FWIW, I pull a 26' enclosed featherlight behind my LX, fully loaded, run between 65 and 70 up and down the east coast on I-81, I-77 and I-95 and average right around 7 mpg. I do not find any hill a challenge and that includes Fancy Gap.
That being said I would not hesitate to look hard at an M380, however the concerns that you mentioned are certainly valid.