Brew Kettle for all grain

I want to start doing 10 gallon all grain batches.

I was thinking that I would need a 20 gallon kettle. I know, a 15 gallon would probably work, but why get 15 gallon when you can get a 20 gallon right?

My concern is the valve. I have heard that some people have had problems with burning their valves up, because the valve is to close to the burner.

Is this a real problem?

Should I get the valve placed up high on the kettle, and use a dip tube?

Anything here I am over looking?

Thanks,
Grossy

All you have to do is have some sort of flame shield below the valve (and thermometer/sight glass). Some folks just use aluminum foil, other use sheet metal, i have some plate welded to the brew stand where the plasticy bits go.