A hot plate, dedicated to just chemistry uses, and never for cooking food, and used out of doors should be OK.
You can probably find a reasonably cheap earthenware dish, to slowly evaporate the concentrated solution, and then roast the salt. Pyrex glass would be ideal. Again, dedicated to chemistry, not for cooking.
I'd be a little leery of someone roasting a nitrate to decomposition. But perhaps there are references tat say that the decomposition of nickel nitrate isn't likely to explode. But that's all the more reason to go with an electric hot plate, away from structures, instead of an open flame.