I hear woods and well demarcated, spreading, pruritic rash and I think poison ivy

Another way to get there: here's no fever but he is v v itchy, so think type IV HSR

Abrupt, sharp line of demarcation, no systemic signs, and mention of environmental exposure should make you think less of strep skin infections

So we're thinking some contact in the forest and we're back at poison ivy or some other allergen

Can treat with antihistamine, but what about prevention? Avoid the woods.

Google bullous poison ivy

Just as another POV, you might have seen well-demarcated and thought erysipelas..but remember that is not bullous. Plus, everything else fell more in line with Type 4 HSN.