From experience Professional indemnity for design work is expensive and hard to find for sole individual. You also need it for the life of the product, it needs to be in place when the incident occurs, not when it was made. You want a specialist single payment plan, Artist to cover or step away.
I don't doubt that this is the case but surely logic says the insurance that was in place when it was made and installed should be the policy to cover. No wonder it’s so expensive, potential life span of 20years say, I guarantee there would be an incident of some description involved.
Somebody needs to put an end to this claim rubbish. If you walk into it or fall off it it’s your own fault, not the guy that made it or put it in.