An alternative solution is as you suggest Ian fitting a battery isolator (red) switch which I have had or have fitted myself on my three cars over the 17 years of ownership and have never put a charger on any of them.
The longest I have left my Plus 8 dormant due to a long holiday was 10 weeks and she fired first pot up.
I would never feel comfortable without a battery isolator switch in a Morgan but that could be due to a lifetime of working with electronics and seeing the resultant battery explosion due to a top quality battery charger failure on standby generator plants on one of the radio stations I commissioned.
Float charging is out of the question for me, but each to his own as they say as I have said previously on here.
