When I was doing this last June, I learned (in advance thank goodness!!!) that my credit card car rental insurance did not extend past a rental greater than 14 days!!!
I ended up returning one car and getting another one, to cover myself. I used National EA both times, so it was extremely easy to do (aside from a side trip to the airport!). The guy checking in the first car looked at me a little funny, though!!!
Patti