Like you, not sure they are rare, but have always heard that rain wrapped tornados do tend to be more powerful...not sure if that is right.
Glad to see our Freeper experts getting in on this thread though.
Rain-wrapped not necessarily stronger, but harder to see. Once they start pulling in rain, they usually begin to weaken. Boy Scout camps are usually poorly funded and structures are relatively primitive. An EF2 would be more than sufficient unfortunately. Rain-wrapped is dangerous as you have to rely solely on hearing it coming. They had a 12 minute warning, which is pretty good - but not many places to really hide from any storm of moderate strength.