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Andy, Here in the US RCD are more commonly know as Ground Fault Circuit Interrupters. GFCIs A US version is pictured on the left.
The easiest way to deal with shore power here would be to have an outlet in the connection box area connected to the shore power and simply move the plug from the inverter to the shore power outlet and turn off the inverter. Similarly have an A-B switch with one input from the solar charger and the other input connected to a shore power charger. And manually switch to shore power when you are hooked up to shore power.
I do a similar fudge recipe except I use 1/2 Cup of peanut butter instead of butter. I melt the chocolate with the sweetened condensed milk in a pan on the stove. and add the peanut butter last. For nuts I will use crunchy peanut butter.
I have been making sparkle balls. The sphere is created by plastic cups glued together with hot glue and a Christmas light inserted in the bottom of each cup. There is no chicken wire needed.
The bamboo cases are out of stock from the supplier you listed.