Just an update on my research into cost effective tire loading options.
First, CaCl2 is more expensive than I originally thought and would cost about $30-35 for a 50lb bag. Need 3.5lb per gallon for -35F so that means $250 for material.
Second, the methanol mixing is a bit trickier than I originally thought. You need to mix by mass (weight) not volume. Methanol weighs 6.6lbs/gallon while water weighs 8.3lbs/gal. That means that to get a 40% mix of methanol and water by mass, you need, by volume, 50% methanol and 50% water. A 40% by mass methanol/water mix freezes at -40F. If you dilute methanol even a little further, to a 30% by mass mix, your freezing point is only -15F.
Third, generic WWF is often rated at -20F freeze point but they don't really state the composition. Methanol is the expensive component so I wonder if these companies are scrimping. They don't need to add much additional water to leave you with a fluid that will freeze pretty easily.
Fourth, it is obvious that 75% tire fill with RimGuard or CaCl2 will add considerably more ballast weight than adding 40% methanol. I haven't calculated the difference exactly but it is about 30%.
Fifth, I have found methanol in 55 gallon drums for only $149. Shop around.
Conclusions to date: 1) best solution: have the dealer load with RimGuard before delivery, 2) CaCl ain't cheap but there is a good reason it is still the most popular Ag use ballast and the corrosion problem is often overstated. 3) Generic WWF is iffy for anyone in an area where -20F is a realistic possibility. 4) 50/50 methanol/water by volume looks like a pretty safe way to get a real -40F solution but the weight it adds is only about 7.5lbs/gallon which is less than water and much less than CaCl or RimGuard.
I'm leaning towards the 50/50 methanol/water solution but haven't done it yet.