Filler on valve covers?

I'd like to hear from those of you who have used a filler on your valve covers to even things out or to cover welds that you don't want to smooth-out completely. I'm dealing with sheet aluminum (fabricated) valve covers which will make thermal expansion even more of an issue (the expansion difference between the filler and the aluminum is a concern).

I know about Lab Metal as a high-end, high temperature solution but what about fillers with glass added, or even regular bondo type filler over urethane primer in this application?

Thanks much, EM

Filler is probably not a good idea on valve covers. You have to consider the rate of expansion on the filler materials vs the rate of expansion of the aluminum. Expose this to heat too many times, it seperates, then you have filler shaking loose on your valve cover. You would be much better off either leaving your welds rough, smoothing them yourself, or buying a set of valve covers if your looking for apperance.