I don't work in such a hot environment but a solid working surface that I like is a solid core door blank suspended by cheap saw horses from Home depot to strengthen the door even further and to raise it a bit would be to take 2x4's and screw and glue them on edge to the front and rear areas of the door it serves like a I beam and insures the door won't sag in the heat.

as a aside here is a cheap and effective air conditioning system https://www.youtube.com/watch?v=HxSLbpAwibg he also has some versions that are slightly different in construction but really efficient for a fraction of what a air conditioner costs.
he also has a swamp cooler set up also working in a 100o hot box just doesn't sound like any fun at all