To my surprise, Nobody was aware that we have always been able to create Horizontal portcullis and sideways sliding gates (using bridges), So I spent this evening creating tutorials.

At /warp gates I have replaced a gate with a Horizontal portcullis gate in the open style as the others so you can see how it works, this is not limited to maximum size.

Next to /warp bridges I have created a sliding gate made from bridges, these do not have to be different types of double-half slabs, this is only for representation, they can be stacked to create a sliding gate.

To see how these awesome sideways gates can be used, I have a working version (with signs and access to redstone) if you follow the rail track from /warp gates or /warp bridges, this is a demo of what they can look like.

I have also removed all reference to gold blocks when using gates and bridges, there is no specific power block for them, I allowed the use of any block to power a bridge or gate so that we were not restricted on design!