At my Immigration, they ask for 3 documents from the bank: 1) Bank statement for the last 3 months, 2) Copies of all pages from my bank book with an update from the same day as applying for the extension, 3) A form from the bank certifying that you have had the required money on account for 3 months. Immigration can most likely hand over an example to show to your bank.
Most commonly the term "marriage visa" is used for a Non-O visa extension on the ground of marriage. If this is the case, then there is no insurance requirement.