okay, so got a few supplies today for the background creation, going to go for the expanding foam and silicone method. Should i only cover two sides and leave one spare for the heater to go on (outside of the terra) ? also for any UK based people reading, been told that door and window sealant is the best to go for regarding silicone, is this safe ? Unibond UPVC & Wood Exterior Frame Sealant Brown 310ml, 5010383236717