Extendable Post
The Sky's the Limit.
<&postbase>Used as the start of the custom-sized posts.
(See <link;immersiveposts:usage;§1Usage§r;start> on how to use it.)

The base can be hidden simply by holding a block in your hand, rightclicking and it will pretend to be that block.<np>
Sneak + rightclick removes the cover.

It only accepts solid and opaque blocks as cover however.