Our 40 ' widebeam Sea Otter is fitted with a Zinc Saver II Galvanic Isolator (30 amp) certified to ISO 8846 and part of the original spec so far as I am aware. The boat was built late 2003 and launched 2004. Since buying her in Dec 2015 at Littlehampton we had the hull surveyed and checked with no faults or pitting observed at all before taking her across the Channel onto Calais and south of Paris. On pulling out for wintering on the hard in Central France we again had the hull jet washed and checked before blacking and it was in excellent condition. However this may not be the same for all Sea Otters as this was a commissined by the original owner as a particularly high spec widebeam and only a few were made to my knoweldge. Having said that we have previously hired a 46' narrowboat Sea Otter in Cambridge which had a similar device. Zince Saver II as fitted was manufactured/ supplied by Professional Mariner LLC in California and the origiinal spec leaflet in the noat file is dated 1999, however it would appear that Sterling may have taken them over as they sell an identically named model widely available on ebay and the internet through yahct brokers.
So far as condensation is concerned we have had issues in the wheelhouse which has stained some of the joinery but managing the ventillation definately makes a difference ad we have stayed aboard in winter weeks without problem. A karcher window vac is also handy and works brilliantly! The boat has Webasto warm air on a 7 day timer with thermostat which works well.
So far as stability is concerned we found her remarkably well planted with its water ballast she weighs about 20T in the water. ( The fin keel as makes a significant difference IMHO). We have had no issues at all on the Channel crossing despite it being very lively at times, nor on the Rhone or the Etang de Thau in the Camargue which is a 17km open water lake right on the Med where we encountered some serious wind. The boat has 'flap valves' as described above and is rated as a Cat C, although we took the precaution of sealing the other two flaps (the cat flaps) on our channel crossing!
Hope this helps.