PradOz replied:

one of the upmarket caravan builders i seen at the rosehill van show had a shelf that hung down off the top rails of the annexe. it was portable and basically had hanging straps with a clip on it that were attached to shelf and it all just hung in place. they were a bit pricey i thought at around $70 each

JJ replied:

At most $2 shops or Ikea you could get 'hanging' canvas shelves to hang from wardrobe rail, which you could hang from tent spreader bars... or maybe you could modify it to hang from tent centre pole by clamping a horizontal rod. These space savers come in jumper size or shoe box size collapsible stack of 4/6 shelves. If cardboard shelves are too flexible, reinforce with thin aluminium sheeting. Hope this helps.

Member -Signman replied:

Why would you want to hang a laptop (computer) in a tent ??
I thought the idea of getting out & about was to leave all the trappings & crap of modern society home- including computers !!