Hill House Hammond used to do a policy with a Lloyds consortium (can't remember who) specifically for ICE insurance. I paid about GBP 36 in 1991 to cover up to about 3,000 worth of gear, which had to be a "fixed installation" (this was before removeable radio fronts, etc.).

In NL, we have a contents insurance which covers all our cars, up to a value of (I think) Fl 5,000. Hmmm. Maybe I should get this verified....