So only 4 pieces with some pins to pack inside a box. Remember the best packing puzzles almost always look easy and almost always have very few pieces :)
Soon you will realize that putting the 3rd piece is impossible or difficult if you try to pack in a "standard" way the pieces. Sliding pieces will be needed!
For such puzzles when it's not easy to put your fingers inside the box to move the pieces, I always try to make the shape with the pieces outside of the box. Think out of the box makes sense here.
Then I see if moving pieces can be done inside the box, and if not then I try to find another shape with the pieces.
Many more moves than expected will be needed to solve the puzzle, with big "hah-ha"
For me this puzzle really embodies the perfect packing puzzle: challenging but not frustrating with an unconventional way of solving it.
I am sure you will like it as much as I did. It appears in my top best packing puzzle.