Yes, I think you should be able to hook the negative to the engine and then just jump the wires.
Have you tried turning the engine by hand?
Never heard of a motorhome without an alternator. Does it have an alternator bracket? You'd think it'd come from the factory with an alternator.
14 yrs is a long time. If it resurrects there's a good chance it could serve as the basis for a new religion.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13