I don't know about skelp, but Kist (or Kiste) is the standard Germanic word for a chest or box - you'll find it in German ,Dutch, Danish, Norwegian, etc etc.

In southern english the 'k' sound often becomes 'ch' while remaining a 'k' in northern dialects (including Scots). So kirk becomes church and kist becomes chest.

I reckon your Gaels nicked the word from Saxons or Vikings, rather than the other way round