i've used this method a number of times.tape off any holes that would let any air in other than your entry & exit holes.tie a small piece of plastic bag in the form of a deflated balloon to the end of your pull string.put plastic in one hole place shop vac on other hole.after you suck you string through tie on wires wrap with tape,and your ready to pull.i did this when i built my house,barn,car stereos,lights on rollbars,