Prosoco Fast flash.
3 tubes left over from siding and window project. $20.00 each.
Flash around your rough opening and doors for tight weather seal.
I really liked using this product and prefer it over flashing tape.
I installed new windows with a nailing flange so I used fast flash for the opening and flashing tape on the nailing fin for a good seal.
I have the sausage gun also available in a separate post.