I'm working on a project where I'm embedding an arduino inside my car door. I'm not sure how wet it may get inside my door, if my window seals are imperfect, etc. My project needs to be as small as possible, and I suppose water-proof. What is the best way to achieve this? I've seen electronics such as flash drives and usb-to-something adapters where the whole board was encased in epoxy, or something like rubber cement or something else. Could an Arduino Nano operate this way without heat issues? Is there another solution that may be better?
Google 'conformal coatings' you might also consider adding a heat sink outside the coating.
A conformal coating looks like a layer of (usually clear) paint over the completed board.
Also google potting, which is embedding the entire board in a gob of something the way you describe. The consistency of the stuff varies from gummy/greasy/waxy to (more typically) completely solid.
-j
Also consider a waterproof box. You can get them in various sizes on the internet. As a matter of fact, most Wal-Marts have two sizes of them in their camping gear areas.
Wow, thanks everyone. I appreciate the point in the right direction.
Franklin, do you mean putting a heatsink over the coating, or having a heatsink directly attached but protruding from the coating (partially covered)?
I suppose I'll have to wait until I build is finished to see how hot it will be. I'm developing on a Diecimila, but the final build will be on a Nano.
I finished my software tonight, I'm so happy. Now I have to wait on parts. 
Regarding the amount of water in a car door.
Yes it can get very wet. They are designed so that any water getting in is held behind a plastic sheet protecting the door card and the water runs out of a drain at the bottom.
Gordon
Thanks for the info Gordon. I kind of figured, but I wasn't really sure. Now I know for sure I need to waterproof this thing.
Since I don't have all the parts yet, I don't know how big it will be.
It looks like MG Chemicals has some different potting compounds, including thermally conductive.
http://www.mgchemicals.com/products/potencap.html
I'm sure there are other places, (hopefully some local) but this definately gets me in the right direction. Thanks everyone.
http://www.otterbox.com/waterproof-cases
This may be a better option, if you use epoxy it will be nearly impossible to remove it if you need to add or remove anything from your arduino or even reprogram it
A waterproof case is removable, reusable and will allow easy access to your board to make changes if you need to
Once you put the epoxy on you're pretty much stuck with it, quite literally most of the time
Some of these epoxy compounds or so strong they are used to make electronics virtually tamper proof
A low cost alternative to the otterbox might be a heavy duty vacuum or freezer bag with a large bag of desiccant inside and a custom made gasket for the wires to the outside world
