Anybody got an opinion on the best caulk to use for exterior wood or Hardie Board? Ive tried using both latex caulk and polyurethane. The polyurethane lasted longer but seems to attract all sorts of dirt, even when it is top coated, and sometimes shows through the top coat when the topcoat starts to wear. Most of the joints are pretty narrow, but sometimes Im caulking gaps up to 3/8 wide. What tools well and also holds up well? Thanks.