Cdrw,
Every border is slightly different and all the above in some variation have happened to me over the years. We used to cross unregistered for free, then it was a B1000, then it was you needed a Import duty paid paper, then you needed a green book in your own name. To do it "with in the law" takes some research as the laws change and/or the border customs don't know the regs and/or have been told to toe the line and do the paper work.This is Asia you might get away with no papers for years and then one official who has been reamed by his boss decides that you are in the wrong or needs money for his mum's funeral ,insists on all the correct paper work, and then you are f**ked.
Ref: Bill.. You cannot stay long term on a temporary export, you need to keep re-crossing the border, after a while even the local police will notice.
Ref: Sihanoukville, if you check the current situation there it is no rentals or no no plates and they are checking papers AND taking bikes.
Ref: Harrythefinn: correct legal details (from personal exp)
Ref:****Hmm...: He needed an export paper to get out of Thailand, there is no exit out of Hat Lek without the correct papers nowadays, Cambodia side can still pay but getting difficult.He is correct that exiting Cambodia the Cambodian customs rarely if ever ask for any Cambodian paperwork.Usually it is only a stamp on the back of the Thai paper, some times a seperate form.
Ref: When I did...: In law it is the same overstay fine for temporary export vehicles as with people overstaying a visa, if the customs guy doesn't know or care on re-entry you get away with it.
Take your pick, like I said they are or were all valid at some time or at some crossing point, if you have most of your ducks in a line then most of the time you will have no problems.
Hope it is clear as mud now.