Daniel McCauley designed a Canon DSLR PSU that runs off 12V DC to 8 to 7.5V DC out. Someone posted a link before and I looked at it and said it's ok but doesn't have over voltage/current fold back or protection.
I'll post the link again
here.
I suspect the cct can easily be modified to incorporated overvoltage protection etc.
In any case I have re-thought the cct and I must admit that the regulators used has good thermal & inbuilt protection thus adding extra protection is probably an overkill.
The only thing I'd do is add an overvoltage protection zener or SCR cct to shut it down if the output raises too much...otherwise I see it a a good'un, especially his 2nd cct (due to it's high efficiency).
Last thing is you need a old canon battery so you can hack into it & pull the internals out.
Anyway...it's worth a thought.