Since the LL design has the 120mm fan sucking the hot air out of the box, i was thinking to use one of those small battery powered vacuume cleaners I think it would do the job very well.

I dont plan on using one, i just thought it would be a good idea if you cannot use fans for any reason.

I think it would be excessively loud!

Every portable vacuum I know of uses brushes for the motor which is one of the reasons they're so loud. You can get brushless DC and AC equivalents. I'm thinking it's unecessary though.

I thought about running an exhaust shop vac up in the attic, then running lines up to it from the PJ. heh

the duty cycle will be too low, those things aren't made to run for hours and hours on end, and you will burn it out pretty quickly compared to the brushless 80 and 120 mm fans.