Here's my procedure that seems to work good for me. I don't use heat pad, jut the baggie method.
1) I use coco coir, works the same for my citrus seeds. I soak seeds in water for a few days until the seeds are very clean (rinse/wash each day).
2) Before putting seeds in baggie, spray with diluted peroxide, clean, then put in baggie with coco coir.
3) Watch the bag with seeds, if you notice any mold/fungus, remove all seeds and wash/clean, put back in baggie with new coco coir.
4) Once I see the seeds growing (roots/leaves) then I move it to larger container/pot, put it outside and put screen over the pot so birds/bugs don't eat the fresh leaves/roots.
Pummelo seeds seems to grow much faster than other citrus seeds. I will need to try Ilya11's method with perlite.