For further info, the fridge slide I'm looking at is the Dometic/Frontrunner item for the CFX3 55IM (already have the fridge).
Dometic CFX3 Slide 55/55IM - Fridge slide for CFX3 55/55IM
www.dometic.com
The platform depth of the storage system is long enough for this (25mm longer than the slide assembly). My idea was that I'd mount the slide to the storage system using the T-slot on the left and rear (front when at the back of the vehicle) which would give 30mm clearance at the front (rear of the slide) to clear the angled back seat.
With the slide being designed for the Dometic CFX3 55 there is 4 mounting points for the fridge in the slide (though the bottom) so you don't have to use straps through the handles to tie the fridge to the slide, though I'd like to use them as well given the corrugations I often drive on, worst case I may have to remove the rear handle to clear the seat and only use the front handle to put straps thorugh for additional security.