Green’s Dictionary of Slang

trunk n.1

[idea of its being a chest filled with treasure]

the vagina.

[UK]Chapman & Jonson Eastward Ho! II ii: I am now free, and now will justify / My trunks and punks.
[UK] ‘Cuckolds Haven’ in Farmer Merry Songs and Ballads (1897) III 41: A woman that will be drunk, / will eas’ly play the Punck; / For when her wits are sunk / all keyes will fit her Trunk.
[UK] ‘Woman’s Dial’ in Gentleman’s Spicey Songster 6: So with grape-juice contrived to make their dad drunk / Then each of them got him to open her trunk.

In compounds

trunk work (n.)

casual or clandestine sexual intercourse.

[UK]Shakespeare Winter’s Tale III iii: This has been some stair-work, some trunk-work, some behind-door-work.