I've been watching through hole film caps disappear. I've used a bunch of these in thermal control loops,
Still making 'em, but I'm seeing a lifetime buy in the future.
The current project will again need thermal control.
Can I use a ceramic X7R as an integrator? Maybe one of these (50V 10uF), http://www.digikey.com/product-detail/en/CL32B106KBJNNNE/1276-3387-1-ND/3891473 I'd run it from +/- 15 V supplies. Time constant no more than one minute.
The question really is, what's the leakage current, and what's the voltage, temperature dependence?
I can hear many of you saying "George, get with it! and get a uC."