Building a fort refers to the act in which you tie up or other wise restrain your partner in a sexual manner.
Greg "Hey dude can I borrow some rope?"
Tom "Of course. But why do you need rope?"
Greg "Well Samatha and I are building a fort tonight."
Tom "Ohhhhh okay just don't get any stains on it."
A port-a-fort is a poggers epic metal tower that can be carried with you in frotinet. When you throw down the port-a-fort a long sexy metal tower will be placed down and you can go inside and go on bouncy tires to have epic roof sex and kill ugly curry munchers
An inconspicuous term used to notify friends that you had intercourse for a long period of time. That you figuratively just "camped-out" at her "site".