We have had an E3 running in our 60' since August , the overboil protection as ready installed by Kuranda is fine- I wouldn't try to "improve" on this. As already mentioned, it is a good idea to fit a separate Fire Valve - also as supplied by Kuranda. We have a Jabsco 8-24volt circulation pump -also by Kuranda** - I am absolutely delighted with this, it is TOTALLY SILENT, can be plumbed in a straight line ( whereas many other circulation pumps have in/out at right angles and necessitate a completely unecessary angle in the pipework), draws almost no power (fraction of an amp),the flow rate is adjustable to suit your individual needs, and is rated for continuous use , the downside if you like is that it costs something over £200.00 -- I consider it to be well worth it!
We have found that flue length -v- oil valve setting is crucial to efficient running but once established it can be left to do it's thing and can be "adjusted" by changing the length of external flue if needed - altho. at the risk of stating the obvious - the higher the setting the greater the fuel consumption!
Hope this helps!
** N.B. I have no connection to this company ! -no axe to grind!