Help making a gate

[Breezy]

So I want to make a gate made of mid-textures that you can't go through, however when you lower them, you can go through them. I've tried using self-referencing sectors and invisible platforms that were seen in TNT Evilution's MAP09: Stronghold, however I'm stuck. Does anyone know how to accomplish what I'm trying to do?

[rouge_means_red]

This is how I've done this before:

 

Sector A contains the MID texture (not impassable) as a line in the middle of it

The thin sector on its left (B) is a raised floor that serves as a wall. It has no side textures and will be invisible in game

Both of the sectors have a corresponding dummy sector, connected to a sector with a very low floor (-200 in this example)

A line action lowers both floors to the lowest adjacent floor