¿To cleanMMM?
 

I usually use my E-maxx off road.

When I return home the clean thing with gun of air.

... but I see as, almost always, he/she finds me some small stone blocked in the superior grill of the box.

What I think is that smaller (and powder) stones will enter to the interior of the box.

Would it be convenient to open it from time to time to clean it?

A greeting.

I'm sure it would make it easier to clean if it was opened up.

Just be careful doing it.

And maybe add some type of fine screening over the air vents to keep out the smaller stones.