Do you mind me asking why you went with fan LEDs? I actually just put fanless LEDs in my 16 Trax last week and I did put the dust covers back on. Just curious to why you chose fan LEDs over fanless. I don't really know if there is a better option or not.
If the round bulb covers you are asking about is the black dust cover that you had to unscrew counter clockwise and screw back in when you were done, then yes, I would definitely put it back on. It is the dust cover so it does exactly that. Can also possibly block moisture from getting inside the housing. Most covers don't fit on the Trax especially after putting in fan LEDs. The covers fit back on my fanless LEDs pretty snug so I am really surprised these do fit back on yours.
Seams like it would defeat the purpose of the fan though. You'd be blocking the outlet and air you could recirculate would be warm or even hot air from inside the head lamp housing. I would leave it off, the fan is going to blow any dust out if it turns the right direction.
Traxy - I've heard mixed reviews of that affecting it or not. Valid point though, thanks for adding that in there. Also, missed your comment from earlier. I just went on Amazon and was curious about some of the cheaper LED options. They are nothing special but definitely cross everything off my list, plus I live in an area for free same-day prime shipping so I was checking that out too. Both the headlight and shipping impressed me
I can't post links but they are the BEAMTECH H11 LED Headlight Bulb, 50W 6500K 8000Lumens Extremely Brigh H8 H9 CSP Chips Conversion Kit. Never heard of Beamtech so I was curious.