Never installed it but here is a little trick we use on clapboard butt joints (other than caulking and good nailing).
Make a piece of vycor or ice and water shield (adhesive backed rubber membrane for waterproofing roof/windows etc- flexible flashing- vycor is the best for side wall applications since it is the thinnest) that is slightly larger than the hardi is tall and about 6" wide. When you nail a piece of siding on leave the side that will butt the next piece unnailed and slip the piece of vycor (with paper backing peeled) behind it so half of it is exposed and the bottom is over the piece of siding below. Now finish nailing and move on to the next piece.
This just makes a backup for when the siding moves or the house settles or the hurricane blows the rain up instead of down and makes sure that any water that might get through is brought back out rather than free to run down your tar paper or hosue wrap and rot your sheathing over time.
It is a lot more work, but it is necessay as all of these products move, even the plywood they are nailed to. Start by making a bunch and then they are ready when needed.
Strive for perfection...Settle for completion