I just completed a fan mod for my V Force Grill.
I installed two 16mm x 4mm 3 volt fans inside(not on top) the mask.
Directly under the vented top section. The only noticable difference from the outside is the very small zip ties used to hold the fans in.
The fans are currently powered by 2 sets of AAA batteries run in parallel inside a remotely located enclosure with an on/off switch. A little modding to the case was needed to change the connections in the case from 4 batteries in series equalling 6volts to 2 sets of two in paralell at 3volts each.
This set-up costs a little more, but it is completely protected, effectively prevents fogging and is nearly silent.
I'll post pictures shortly.