Here's a simple tip. If the RV antifreeze says "WARNING:COMBUSTIBLE" walk away. A propylene glycol product is not flammable but one made with ethyl alcohol is. This cheap product is a blend of ethyl alcohol and PG. Choose a product that does not contain alcohol.
When in doubt always read the labels. Do not be tempted by price. Ethyl alcohol blends can be had for as little as $1.99 to $2.99 per gallons while a typical price on a propylene glycol -50F rated product is about $4.50 - $5.50 per gallon..