How do I plan where my caterpillar tunnels go each year?

Place each tunnel season by season, and your rotation is written down for you: move it next year and last year keeps where it was, with its plantings. Create each tunnel once, then edit the field block it covers, open the Tunnels tab, pick the Tunnel, and set the Starting bed and End bed.

A tunnel sits on one block per season, and two tunnels cannot overlap. Growing locations lists each tunnel with the block and beds it covers this season.

See Add tunnels to your field blocks.