Potting epoxy is not a good water barrier. Silicone based products are usually superior. Conformal coatings may meet some of your needs with subsequent encapsulation in a product aimed at mechanical protection.
Coatings of silicone do not block water 100%. What is not widely understood is that NOTHING that is used as an add on coating blocks water 100%. [There is a special coating - Parylene and similar names - applied via vacuum deposition of vaporised coating which changes its molecular arrangement during the process, which is as good as you get, not perfect and very much not a do-at-home treatment]. BUT water permeates through and coating. A good coating works by having very low % water dissolved in it and by forming an aggressive voidless bond to the target. This means mainly only water vapor is present and lack of surface micro-voids which can form liquid water pockets means corrosion rates are far far far lower than otherwise. More on such below.
When applied as an after-market treatment ALL conformal coatings have the potential to degrade performance or do damage. This is usually at the "obvious enough" level - use your brain, look carefully and think ahead. Covering any screen with a coating will usually be a bad idea. Getting goo that sets on any electrically connecting surface will be a bad idea. If it is meant to move (hinge, keyboard flexure, ...) then gumming up the motion is liable to be a very bad idea. Sounders/beepers/speakers that make noise may make different noises if plastic coated. Thinks that get hot and are cooled by air movement usually get hotter and are less cooled when coated. Holes that allow airflow may vanish ... . Once such 'little things' have been addressed, a range of coatings MAY help.
Dow Corning make a material named Dow Corning 1-2577, which does a better than most job. It can be brushed sprayed or dipped and air sets to about a 0.1mm layer. It is not cheap, contains enough volatiles to be used in a fume hood or outdoors and you are unlikely to see it in retail sales. A "low VOC" version exists.
Dow Corning conformal coating products here
Dow advertised a PV6100 material a few years ago that sounded like it would be ideal (aimed at solar cell encapsulation) but they have "gone all quiet" re it recently. May yet be available.
The older Dow Corning "Sylgard 184" is much used by the DIY PV panel manufacturing community with good reported results. Also see slower setting Sylgard 182
Note: I have no involvement with Dow Corning, except as a satisfied user of their products.
"Silicone spray" will provide a degree of protection against water but is far from ideal.
Clear polyurethane plastic spray (sold as "lacquer" or "clear varnish") will do a passingly good job as an aftermarket conformal coating. You could spray in an excess and let it run to and from over semi inaccessible surfaces.