i don't think i have ever seen any...but many companies give new for old cover insurance on caravans anyway, so this negates it.
the most i have ever seen is to cover up to a 5 year old van.
we actually had a total loss claim a few years back on a nearly 3 year old van...we got full sum insured...i.e. purchase price of a like for like replacement.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.