Just been reading this thread , Might i suggest the use of reverse osmosis water from an aquarium shop , way way cheaper than distilled water & no drawbacks

I always use RO water to top up or refill empty systems as there are zero salts or whatever's that cause deposits in engine .

Toyota insist on the use of deionised water to fill /top up their cooling systems for this reason

Well, I finally got round to doing the fluid change today, and have to say it was not a bad job.
I spent an hour or two making up adapters to connect a couple of short lengths of garden hose to the caravan heating pipes (22 to 15mm end flow reducers fit perfectly) and used an old Whale pump to push the fluid through; the actual flushing and refilling took about an hour.
Bleeding the system was a little difficult as the height difference between the header tank and the top of the bathroom towel rail is only about a foot, so there was very little head to push the trapped air out, but a little perseverance saw it done.
In total, I used 15 Ltrs of deionised water (Wilko’s, £1.25/ 2.5 ltr) and 5 ltrs G13 antifreeze from my local motor factors (11.60) to complete the flush and refill.
Caravan dealers are charging up to £200 to do the job.

you could us that waterless coolant stuff with no water in it at all

https://www.evanscoolant.com/how-it-works/

looks good