We dont have the JOOLCA.
We have an AN-MENY unit similar to the Joolca style units .. Nice and hot showers [ had steam coming of the water ] even with the late
afternoon outside winter temp of 19* C in the shade and a 20 knt wind blowing ..[ open air alfresco shower
] .
Ours is an 8 liter PM heater unit that provides a good [ though not as strong flow as home, but equal to the twine set up we had ]
Flow rates set at 40 / 42 deg C gives A nice hot shower, and is a bit over 4 ltrs per minute through the shower unit ..
At 8 ltrs per minute the water would basicaly be luke warm .
Heater unit is hung on a pole driven into the ground beside the ensuite shower with a 4.5 kg gas bottle underneath it
We use a 12 ltr pm pump and it empties a 25 ltr drum of cold water in about 6 minutes ..
We use 4 x 25 ltr plastic water drums for ease of resupply and portability for the shower .
The pump either gets hung on the bull bar or the shower unit pole and power for it is through the front mounted Aux power anderson plug
If you wanted a bit more flow a 10 ltr p/m heater unit might give a bit more, this one works fine for us.
Though we did find it pays to recycle a bit of water at first through the shower head to purge air out of and prime the heat exchanger so as you dont waste any water or get bursts of realy hot water till it primes, if its been empty for a while .