Cover the tail surfaces FIRST. You want the kit to look like an ARF before you start gluing the tail on. Cover the fuse too.

There is a LOT of dry fitting and test fitting involved with kit building. I usually end up dry fitting a kit 2 or 3 times before it's done.

Once the fuse is covered and the tail is covered, you can glue the tail on. Those filler blocks should be covered too. Once the tail is glued on, cut the covering off the vertical stab and glue the blocks into place. Just like an ARF.

Covering the tail WHILE IT'S ON THE PLANE is a HUGE PITA You need to do all your covering BEFORE you ever get the glue out.

Good luck.