I have searched the internet extensively for an eloquent solution, but most of what try to pass themselves as "answers" are actually unreliable and use dodgy conversions.
So, when everything else seems to fail, I turn to ExpertsExchange ;)
Basically I am after using something along the lines of:
where min and max will be defined by me and of course must fall in the range of UInt64.MaxValue and UInt64.MinValue
(instead of the standard random.Next which returns an int)
This method MUST be in a position to potentially get any number within that range and not fail to do so due to conversion errors!