You’ve got a few options Wayne.
Here’s one : https://purefreedom.co.uk/products/pure-freedom-hot-water-system?variant=43450458472622
You’ve got Xline and Grippatank as well. Probably a few more that others on here may recommend.
I’ve got a Grippatank system, had it a few years now and working well. Been very reliable. I get upto 60-67 degrees on full from the heater. So you’ll lose a bit as it travels down the hose in winter.
You have the choice between a 5.2kw Webasto (single operator) or a Webasto Thermo Pro 90 9.1kw which replaced the 90S and 90ST diesel burners.
The specs for the Pro90 and the 90S and 90ST are the same.
We still have Varistream controllers. My 2 man Heatwave will just manage heating the water for the first operator to 55 degrees and the second to 50 degrees - both temperatures are as the hot water leaves the heater. Any higher than that and the burner wouldn't keep up.
Operator 1 (me) uses microbore hose and my son uses minibore on the other hose reel. When the ground is very cold, the temperature of the water at the brush head can only be called lukewarm at best. I run my flow at 3 which is around 30 on the Spring controller range, where my son uses 2 on his. Believe it or not, the minibore on his hose reel seems to retain heat better than my microbore.
Last Wednesday I used the heater to fill our backpack with hot water from my external hose port. At 8 on my Varistream, the heater wouldn't keep up with the heat demand of 55 degrees. It would manage, just, at a flow of 7.