Dear Matt,
Dug in positions for weapon systems which tactics are mainly based on maouverability such as tanks and sp anti tank systems, are used in prepared defence lines. These positions are prepared by the engineers with the help of shovels (in the Dutch army types derivated from civil types like 'Werklust' ) and/or dozer tanks like the leopard engineering tank.
The size of these pits have to fit to the tank or sp gun it was intended for. The gun system is just above the normal earth level, but able to move. Furthermore, the position not seldomly is camouflaged at the enemy's side and for air recognition. Since quite some earth is moved, this is a hell of job!
Do not forget to make a slope side to enable the system to drive in, but also easily out. Dutch centurions and leopards, but also the AMX 13, in the tank battalions I served in as an artillery observer, drove in backwards to make an easy exit in case of need possible. The gun was positioned over the engine deck.