you can get a respirator, they cost 40 dollars. i know, they cost a lot. but why get sintra? do the trash can armor method first. it's easier, and has less hassle. with the trash cans, you don't need to heat it and bend it or anything, just cut it out. it's great for beginners IMO, even though i never tried it.
but if your still planning to stick with sintra... i don't know, it's your choice. i'd recommend the trash can method, but you don't really need to do it. it's just a recommendation.
but if sintra's your way, i think you can also do it outside (which you probably mentioned, with the pot on the grill and stuff). i think you can just boil the water until it's bubbling, and i mean REALLY bubbling, then take it outside and then work with it. i don't know, just a thought.
oh, and by the way hopefull, i noticed you mess up in some of your posts the word "the". sometimes you type "hte" instead. you type to fast?