So in the end i've decided to add two 250v 10A RFI filters onto the output of the power unit/switch with twisted L/N running from the units to the outputs.

12v Trigger wiring MK3-RFI filter.jpg

I've also purchased a larger enclosure, this allows me plenty of space and will provide the option to add other items if i wan't at a later date, including the option to supply the unit with a true 20A rather than the 13A max the plug can supply.

12v-240v RFI trigger unit.jpg