Quite the torture chamber!
An interesting challenge.
1) Any existing holes can become anchor points by sandwiching oversized fender washers on each side of the hole, captured there when the fastener is snugged.
2) Heat-wrap would help contain the infrared.
3) Extra heat-shields with air-gaps.
4) Partial perforation of panels nearest the heat source if necessary.
5) Forward narrow panel, all-metal.
6) One-piece behind, to the rear suspension lower arms.
7) The lower arms themselves could carry their own 'moving' belly panels.
8) Behind those, a single-piece panel with diffuser.
9) Urethane-rubber floor mat material to close gaps.
Just thinking out loud.