How can I prevent, slow or reduce white corrosion build-up on my battery?

I check and refill the electrolytes every few months with distilled water.

There's no earthly reason for you to need to do that.

I use a Battery Tender (float charger) with a wiring harness installed on the battery to easily attach the charger, which I do most nights in winter.

Oh, wait, I take that back.

The problem is, your alternator is a 3-stage charger that knows exactly how to charge your battery without overcharge.

Your battery tender is a cheapie (let me guess, Canadian Tire) that just blasts energy into your battery without the slightest clue or care of overcharging.

See, the battery doesn't need to be charged; it's already 100% charged when you park it. What the battery needs is to be warm. Warm batteries have much more cranking amps than cold ones. What your battery "tender" is doing is heating the battery, by overcharging it.

Hence, all the splashing.

And the problem is, you're adding water back in, but what's coming out is obviously not merely water. The overcharging is causing it to gas off and sputter up the essential chemicals from the battery itself, i.e. the acid. I bet it neutralizes very nicely with baking soda, yes? It's battery acid. That belongs inside the battery, not splashing out.

You're needing to add water because you're boiling off water (and sputtering out acid to boot) because you're overcharging it. And what makes you think the battery tender works is the side-effect of overcharging: heating the battery.

If you want a battery tray heater, then get a battery tray heater.

By the way, if that was not a maintainable battery, the water still would have boiled off, but you would not have been able to replace it. You're not allowed to overcharge non-maintainable batteries!