To isolate or not?

After problems with a flat battery in my current van - a Swift Escape 686 - I have fitted a battery isolation switch which seems to have solved the problem. I am shortly taking collection of a new Auto-Trail Tracker van and am wondering whether to ask for an isolation switch to be fitted prior to collection.

Have any members had experience of having an isolation switch added to an Auto-Trail van? I am aware of flat battery problems with Auto-Trail vans.

My van is stored in a barn at a large storage site so Solar Panels are not the answer. I do not use the van from early December to beginning of March.