Does any one have any advice on what gasket material to use in converted PeeWees?

The teflon ones get pinched of right away so I've tried using a thin aluminium one from a soda can. I got several good runs in today, getting about 10000rpm on a graupner 6x3 when fully leaned out, and the engines sounded really strong. That's on my regular diesel fuel with 33% ether, 25% castor and 1.5%DII, so nothing special, and had very easy starts when priming the piston.

But eventually that gasket was broken too, after about 4-5 tanks. I'm not sure that it gets pinched of, it might actually get bent off (?) right next to where it is clamped. Any ideas? Thicker aluminium or brass instead?