Los Angeles - Gateway Central Garage @ Union Station

I would like to park in the Gateway Center Garage for a trans-continental train trip and a return flight to LAX 18 days later.
Is using the Flyaway bus and parking doable in reverse (train first and fly last)??
Are reservations for LT parking available or is it catch as catch can?
If no reservations, is parking usually available on any given (very early) weekday morning?
Is the place fairly secure for long term parking?

Thanks for your indulgence.

I would like to park in the Gateway Center Garage for a trans-continental train trip and a return flight to LAX 18 days later.
Is using the Flyaway bus and parking doable in reverse (train first and fly last)??
Are reservations for LT parking available or is it catch as catch can?
If no reservations, is parking usually available on any given (very early) weekday morning?
Is the place fairly secure for long term parking?

Thanks for your indulgence.

1. Yes.
2. Best guess is catch-as-catch-can. There are 500 covered parking spaces designated for FlyAway bus users, it is $6/day, limit 30 days, major credit cards accepted.
3. There are no guarantees and I don't know what time, if at all, it fills up. Best guess is very early morning should be OK.
4. The garage is patrolled by security guards.

Thank you !!!:)