In reply to Reginald of Clan Fivetail (msg # 95):
The core rule book says under Mounted Defenses (Page 478) (Playing The Game Chapter)
quote:
"Because your mount is larger than you and you share its space, you have lesser cover against attacks targeting you when you’re mounted if the mount would be in the way."
Your construct is commanded verbally as I understand it since its semi-sentient. An actual structure surrounding your body isn't strictly needed. such a structure would be an add-on to your construct.
It is assumed that you sit on top of your spider when you mount it which makes it hard to fit through a door.