I have mine straped in as my sub did not come L brackets it came with straps.
It does come out ok have to fold the rear seats forward then lift it out at an angal. Or you can build it and cut it it half and the carpet it it two parts so then it it easyer to get out if you want!!! I though would go for form over function as how offen do you get a flat tyre copared to how offen you open your boot??