I use the rcm rear cover, and haven't used anything on the front for the year that I've been using my 1515 (mostly off road racing). No issues yet.
If I was going to use something I'd just cut out a bit of 1mm thick aluminum sheet that I have.

That is what i was going to recommend. I use nothing on mine but a rear cover and it is fine. I have been thinking of a screen but never got around to it.

Magman...listen to lutach he's got it down!

I just use elec tape in the front, and a vinyl cap I snagged at work for the rear. You can actually get free samples of caps if you want and have some "business interest" ;)

The one I have is flanged, but I'm going to get a regular short cap in vinyl. It fits tight, and at worst a drop of CA holds it on. Poke holes for the wires and it will help retain the cap further and seal up tight. Nice as it keeps bearings clean

I have the RCM front cover/mounting plate

http://www.rc-monster.com/proddetail...orcover&cat=20

Electrical tape on the front and the RCM rear cover. I noticed that dust still got in the motor, so I just took both off and haven't had any problems. I think it runs a tad cooler too with no cover. I just blow it out after a few runs with air. This is running on a pretty dusty track.

I run the covers but I think I will leave them off when I run my inferno gt (street car).

i ended up with the tekno neu, but prior to that, i was planning on some foil tape; like the kind they use for HVAC ducts.