My answers biased on my experiences, YMMV, All of these resulted in an approved F1 last year on a trust, and are what I used for my most recently submitted F1 this year on the same trust.
Section 2 - Check Corporation or Other Business Entity when using a trust.
Section 3b - "Name of trust"
Section 4b - Short Barrel Rifle
Section 4e - Length of barrel AFTER shortening, (no advice of length from me)
Section 4f - Overall AFTER barrel shortening, with stock extended
Section 4h - I put "Name of trust city, state(2 letter state abbreviation)" There may be disagreement on this section, some say leave blank other put additional calibers in this section.
Section 4i - Any Lawful Purpose
Section 4j - Check the "No" box
Section 7 - Your signature
Section 8 - Your name as Trustee
Section 13 - Leave this blank.