array of resistors as a heating element
Don't think that will work, most resistors lose the plot around 300C (I once built this jig using two metal clad resistors to sweat some braid to a copper strip and the resistors kept failing, but even the normal ceramic resistors will be struggling to stay together much above 500C).
Quartz halogen bulbs make great heating elements when they are glowing dimly, I used some in a vacuum drying jig , it was only 25 x 50 x 100mm internal volume.
You can buy $$$ nice square ceramic heating elements for rework, and these could be placed under your pcb.
Another option might be to hack up a cheap hot air gun to blow air under the PCB, you would need a diffuser, but it could make for a small oven.
Or you could take some toaster elements and rewire for 24V, but whatever path you take, it's hard to beat a $20 toaster oven from Kmart.
And you can bake out silica gel in a toaster oven, and warm up PCB's prior to conformal coating, and heat up pies!