I am looking for advice from women who have cycled in se asia (Laos, Vitenam, Cambodia) about clothing while on and off the bike. How modest do I need to be while riding? Can I wear bike shorts while off the bike or do I need to put long pants on?

Hello Mandy,
cycling shorts could be possible for some places but they are not very "lady like" in asian (even it wouldn't be very gent' like, too). I think, best choice would be to wear the lightweight throusers used by asian people (look a little like sleeping pants). Take in mind, that a propper outfit is very important for asian people.

Best reguards,
André

P.S.: I think, Cambodia could have some risks (crime, kidnapping) on countryside. try to collect some detailed informations, before you go there.