Thanks to all for your advice.
After reading another thread on this forum, I'm feeling a bit happier regarding the safety of my current setup.
"just unplug the setec from the 240v power point. that will stop it from supplying 12v and charging your battery. By leaving the setec in place it will still provide low voltage cutout protection to your battery and fuse protection for your load circuits"
https://www.expandasdownunder.com/threads/how-to-bypass-setek-charger.2487/
Am I right in assuming that the 15A 240v power in caravan is independent from the Setec unit and is protected by the RCD combo?
All of the above is of course assuming that no other fixed wiring has been modified.
My only other current concern (excuse the pun) is the fact that the battery isolator switch on the wall now does nothing (as it cut power thru the Setec unit).
I guess for the time being, I can isolate battery from all 12v circuits by removing BATT blade fuse from fuseboard on front of Setec. Would this (admittedly rough) idea do the job?
Notwithstanding what @mikerezny said about about what "could or could not" be connected to where @Dirtynidge, the Setec unit is disconnected from the 240 volt supply by not connecting the 240 volt input plug. The Setec is (or should be ) now just acting as a distribution point for all your 12 volt items in the van with power from the battery. Low voltage disconnect should still be effective as this is sensed by Setec from battery voltage. With no charging from Setec and only from Ctek 5A charger which is directly connected to battery, there is no 240 volt potential in Setec distribution unit. All separate fuses are in circuit as well as the 20A total load fuse for all your 12 volt loads. Yes, you could remove the 20A fuse to isolate the 12 volt loads if you wish, but not really necessary unless doing repairs etc.
With the Setec NOT CONNECTED to 240 volt power, there is still the other 240 volts power points working as before and all 240 volts power is through the RCD.