Forge Custom Sealed Deck?

With the current Manalink's Sealed Deck support being a bit unpredictable, I'm looking for alternatives, i.e., computerized versions that let me play Sealed Deck against the computer A.I.
I have now tried Forge and BotArena, both of which have an impressive list of cards and some sort of Sealed Deck mode.
It seems to me that, functionally, Forge is closer to the kind of Sealed Deck play I want (aside from not having a tournament tree - and if there is a way to save and exit the game in the middle of play, I haven't found it yet).
However, just one big problem. I can't figure out how to use Custom Sealed Deck mode.
I like the option of being able to pick the block you want to play Sealed Deck in. But sometimes I would like to try something crazy, like the current environment with an Arabian Nights booster pack thrown in. Presumably the Custom Sealed Deck mode might allow this. But how?
I tried to build a 'Cube' and put it in the relevant directory with the '.sealed' extension. Result: Now Forge crashes when I select 'Custom' Sealed Deck.
Can anyone point me to some 'for dummies' instructions of how to use Custom Sealed Deck mode?
I have now tried Forge and BotArena, both of which have an impressive list of cards and some sort of Sealed Deck mode.
It seems to me that, functionally, Forge is closer to the kind of Sealed Deck play I want (aside from not having a tournament tree - and if there is a way to save and exit the game in the middle of play, I haven't found it yet).
However, just one big problem. I can't figure out how to use Custom Sealed Deck mode.
I like the option of being able to pick the block you want to play Sealed Deck in. But sometimes I would like to try something crazy, like the current environment with an Arabian Nights booster pack thrown in. Presumably the Custom Sealed Deck mode might allow this. But how?
I tried to build a 'Cube' and put it in the relevant directory with the '.sealed' extension. Result: Now Forge crashes when I select 'Custom' Sealed Deck.
Can anyone point me to some 'for dummies' instructions of how to use Custom Sealed Deck mode?