As happens sooooo often with these inquiries, you haven't told us ANYTHING about what you are trying to encapsulate.
Therefore, without knowing anything whatsoever about your project, I would recommend Dow Sylgard 184 silicone encapsulant. Info at:
http://www.dowcorning.com/content/power ... ault.aspif
Its huge advantage over epoxy encapsulants is that the circuit is repairable by cutting away the encapsulant with a knife to gain access to the area needing repair, making the repair, and pouring new encapsulant. This is in extreme contrast to epoxy that is normally impossible to remove for circuit repair.
Sylgard 184 is also water clear (like some epoxies) so you can see where the components are if repair is required. Its weather resistance is excellent.
awright