Solar is for sales people and newbies that haven't figured out better ways yet. Charging via isolator/solenoid and a generator are far cheaper and more reliable. When I was charging my house battery solely via generator, a 5 gallon jerry can of gas would last over a year.
In Europe petrol/gas is more expensive and using a generator can be difficult due to other people being close by
Insulation is highly questionable and debatable.
Again, in Europe insulation is required because it can get cold and damp.