I believe most guys don't for trooping because it would cut way back on the amount of air you'd have circulating in the helmet which helps to keep you cool. Plus not to mention it would trap the moisture and condensation from your breath possibly causing your visor to fog up quicker or more than desired.
There you go. Two different opinions. I don't have any fans in my helmet so I'm thinking that may make a difference too. I'd like to have a fan in my helmet and I tried it once but it made too much noise. What fan are you using in yours Asok? Wow, now I'm curious as to how many people do troop with a helmet seal...maybe I need to get with the program here.
Actually Boba was supposed to have a neck sealer. Look at the Star Wars Chronicles book. They made an attachment that velcroed along the front half of the helmet (under the chin) and then velcroed to the neck of the quilted balaclava they used on the pre-pro suits. They didn't use the neck sealer in the films, but continued to use the quilted balaclava.
Since Jango doesn't have a high neck seal around his throat and just a collar with a balaclava, yeah I do kinda find it silly looking when I see Jango costumers at conventions with visible necks showing from all sides since they don't wear the balaclavas.
I don't use a seal or a fan. I work outdoors and am very acclimated to outdoor temperatures and trooping in it is not much different. I do not wear a balaclava either, though I do have a neckseal. Maybe one of these days I'll make a balaclava from the same material as my jumpsuit to match materials and color.