I like to use 5gal buckets that I have either sitting somewhat cocked eye or have part of the top broken that I place some fine mesh over for overflow to prevent the fish from being washed out when it rains or when I top off with water-since we go through drought in my area too.
I use other items to keep the Betta in-but I like to try and keep them in things that are at least 12-20inch deep-water is always dark tanned.
I place in areas so that they won't get anymore than a few hours of sun-I do want them to get some sun for the plants.
I don't make water changes per se-they either get flushed out when it rains or a bit of over flow when I use the water hose.
I don't cover mine, I add dried oak leaves to the buckets and lots of stem plants that I allow to float and floating plants.
Water temp can get well over 100F and as low as the low 60'sF and then when it rains or I use the water hose the water can dip down to the 50'sF sometimes....never have lost a Betta, fry, eggs...etc......just seems to make them tougher and more tolerant of the extremes.
I have been doing the outside spawns for a few years now and have made a few changes-its never the same year to year......
Last year I had great success too-these fish are a lot tougher than they are given credit for......
We had a mild winter too this year and I have been collecting mosquito larva all winter and have had Bettas, guppies and plecos outside in my 250gal tank since March when usually I can't get them outside until late May/June-had a few days that I had to add heat jugs-but never lost a fish.....