I wouldn't use something as potent as epoxy. What happens if you wish to change the boards. A normal standoff and double sided tape would be the ticket. At least then you can pry it off with a screwdriver without too much damage to the chassis.
Must the standoffs be self-adhesive? I generally avoid using these because over time the adhesive dries up. Also, these tend to be made of plastic and they become brittle with age and break. In either case the board might come loose.