If you're having trouble getting sinkhole coverage, contact Rita Canty with Brightway Insurance out of Jacksonville - (904) 646-1850
They represent a vast majority of the insurance companies that write HO insurance in FL. I'm sure they'll be able to help you.
We got our insurance - with sinkhole coverage - through them. I know of at least 2 other members here on TOTV who were successful in getting their coverage though them as well.
Bill