[Spruce]

I’ve sent emails to various auto electricians over last couple of months , and only had about one reply to at least 6 emails sent. I’m going to try the next county see if any one else will do the job. County next door is only about 10 miles away, Tyneside have received about 6  to different companies and Ive only had about 1 reply .

I would still buy one of those cigarette plug voltage testers and watch what voltage the alternator charges at when you are driving around.

If the alternator charges at between 13.9 and 14.2v constantly, then you can use that cheaper split charge relay kit you linked to initially.

If the charge voltage jumps to any voltage higher that 14.6v, then you have to go to one of those b2b chargers.

Fitters who fit towbars and caravan service workshops are all people you could contact to fit a split charge relay.
Didn't someone say that there is a guy in the north east who fits wfp tanks. If so he should be able to help you.