Regarding the heat source. I had suggested the infrared heat lamps, which seems to me to be the easiest approach, and one that I’ve even seen used in professional machines. I don’t think they even need to be mounted in a box that traps the heat, since the infrared being used is just a frequency of light. But, i’ve not personally done this.
I did run into this video of a guy who used an infrared space heater. Though, his box that housed it is quite larger. Though, perhaps it collapses nicely, and seems very quick to set up. https://www.youtube.com/watch?v=maH5Ech0wK8