Regardless of whether they are available through Sowester or not, they are pretty low down the quality list for boat use IMV. No matter how dry you think your console is, it is unheated and pretty much unventilated. It will
get damp through condensation and that will be enough to cause corossion on the ends. Don't call us for help when your VHF stops working (oh... just realised you won't be able to
There are countless people that consider themselves professional in the boating community. Just because they call themselves it certainly doesn't mean they are. If they don't understand tinned cable and reliability in electrical work then I would steer clear. Sadly alot of this type of problem is down to ignorance and the remainder down to cutting costs. Listen to Cookee - we can vouch for his experience. Perhaps you will question how professional your fitter is when you understand that 8A is twice the current your average set of nav lights would take.
And finally, there is no such thing as a current rating for a cable unless you know how long it is. The maximum current it will take depends on it's length and also whether it is enclosed, bundled with other cables or open to the air to dissipate heat.
Get yourself a BEP or BlueSea panel which will be made with stainless steel contacts and take modern automotive fuses. You can then fit and forget.