I've used the following recipe in baking before. Everything I've made with it has turned out pretty well...
Sweetened condensed milk
Dry soymilk powder equivalent to making 3 cups milk. (3/4 C Better Then Milk brand powder)
3/4 C water
Heat until boiling point. (Microwave works fine for this)
In a pan on the stovetop Melt 6 T vegan margarine on medium.
Add 1 1/2 C sugar
When the sugar begins to melt
add hot milk and a dash salt
Boil gently and stir 5 min.
Cool and use wherever sweetened condensed milk is called for.