Similar set up to what's in my car, I used superstrong strength velcro to stick my sub and amp to the boot floorboard. A few quid from Halfords. Really is strong stuff, make sure you're dead cert about positiong 1st cos its a b**ch to move!
And secure it down ASAP after you've wired up and put it all in. I hadn't had a chance to stick it down after doing it and 2 days later I had an accident and had anyone been sitting in the back it would have caused back injuries.
My amp was screwed in in that pic ^.
Not got current instal pics atm but looks just like yours.