I get a lot of use from
solar showers.
I like the Stearns 4 gallon bag best, it has a large screw cap which will not easily cross thread, nor leak, and seems sturdier than other brands.
I recommend not using the hollow plastic tube for the handle but get a 3/4 inch oak dowel instead. The tube will bend and cause the bag to rip on the edges when hung.
Knowing where the weak points are, I re enforce them with
fiberglass soaked in 'Amazing goop' It does not have to fully saturate to be effective, but bond strength is important, meaning mechanical tooth and degreasing are considerations.
'Summershower' brand makes 3 and 5 gallon versions. I liked the 5 gallon one, never tried the 3, but like the Stearns 4 gallon one best of all that I've tried
Get an extension for the nozzle. I like them close to 4 foot, and thay come with barely 15 inches. These solar showers are in the 25 to 30$ range. All lesser models I have tried have been a complete waste of
money and time.
They need a screw cap or will leak if not hung whilst heating.
I've had one cheapo with an easily cross threaded cap which would leak if overtightened, or undertightened and the goldilocks zone was difficult to achieve when new and impossible later.
I use 12v seat heaters, 25 to 45 watts below these bags to warm them towards that ideal 112.5F. They still consume about 35 amp hours of battery to get 4 to 5 gallons of 65f water to 112.5f, but much depends on the
insulation used above and below, and it takes ~14 hours.
Keeping the already hot bag hot, uses much less electricity, so I will often take it from the sun mid to late afternoon and put it on the heating pad for a late evening hot shower.
The sun can heat the water much faster for free, and I have used both the sun and the 12v heating pads at the same time.