SpareParts Packing Underwear

SpareParts Pete Packing Briefs
Pete Packing Briefs
by SpareParts

Fits a wide variety of packer brands and sizes; lightweight, breathable material; ideal for use with STP (Stand to Pee) packers. S-3X. $39 USD.
SpareParts Pete Packer UnderWear Trunks
Pete Packer UnderWear Trunks
by SpareParts

Comfortable boxer-brief style of underwear (also available in commando, freestyle, and briefs styles), designed for use with most sizes and brands of soft packs and STP (stand to pee) packers. S-XL. $39 USD

Also see: Packing Straps & Jock StrapsThe Great Packing Harness Roundup