This article is way over-kill, they use a oven heating element for heat. You could adapt this to a plywood version.
https://www.powdercoatguide.com/2014/09/how-to-build-powder-coating-oven.html
You can use a battery charger to remove rust - https://www.bing.com/videos/search?q=using+a+battery+to+remove+rust&docid=607991640155357343&mid=4C3D8EB3CD5F93FE9EEC4C3D8EB3CD5F93FE9EEC&view=detail&FORM=VIRE