Making a Glass Negative Carrier

I've been thinking about making a glass negative carriers for 4x5, 8x10, etc.

For a given sized sheet film and two appropriately sized sheets of glass (one which is AN), is there enough weight on the top one to hold down the negative? Or, is it necessary to add pressure through the use of clips or something?

How much pressure? Can too much pressure result in Newton rings, even though one is using an anti-Newton ring glass on top?

I make negative carriers but leave the bottom glass out. It does nothing but provide two extra surfaces to collect dust. The top glass is anti-newton and its weight is easily heavy enough to hold a negative down. When the heat from the enlarger lamphouse hits a negative it wants to bow upwards and the anti-newton glass prevents this.