I just have it done this late afternoon. Don't have a chance to test it out yet, but I am pretty sure it will be okay. I will report back after this weekend.
Thanks to everyone that help me when I post questions regarding poor man's radiator; everyone is very creative and have their own way of doing things...
This is actually a vent cover from home depot! They come in 3 colors! White, brown and aluminium. Size is 16x6. I actually like the aluminium, kind of match the other parts of the bike... Not quite, but good enough for me...
That's all you need and 6 cable ties!!! Total cost < $5.
There are many type of vent cover. The one I used has build in mesh on the inside. Invader is correct. Mounting it upside down like I did will block off lots of !$#!$#!$&&(^ kicking up by the front tire. They have no chance to hit the radiator at all, even small sands wouldn't get stuck in your radiator now.
Ventilation shouldn't be a problem as seen from my pictures. Another important thing is there is a little, very little (2-3mm) gap between the cover and radiator; any find sand that get through that are harmless will not collect at the bottom. They will go straight out from the bottom.
The only thing I am not sure is the cable ties... I know everyone else is using cable ties to tie their protector on the radiator, the ties wouldn't melt... Right? The ties I bought are electrical cable ties.