I would try regular mouse traps, that is what many pest control people use. and if you don't want poison the go with that. the droppings may be old. try a few traps wait several days and then when they are all gone mask up suit up and bag the fouled insulation and re-insulate. I am not sure about the shop vac. may blow lots of dropping dust everywhere. don't want to get the hantavirus. Just make sure they are gone before you reinsulate. try and find as many access points as you can.
Everyone is entitled to their own opinion, but not their own facts