I don't have RTWP, but I have this level in my Sokoban folder. Not that hard.

I did it after my 6th try.
Counting from left to right, from bottom to top:
Row 1: Push boxes 2 and 3 one tile up, and the box 1 two tiles to the right.
Row 2: Push boxes 1 one tile down, and the box 2 one tile up.
Row 3: (created now) Push box 1 one tile to the right.
Row 1: move the box 1 one tile up and the box 2 two tiles to the left.
Row 3: move the box one tile to the right.
Row 2: push the box 2 one tile down.
Row 3: push box 1 one tile to the left and 1 tile down.
Row 1: push the box 2 one tile to the right.
Row 2: push the box 2 one tile down.