Thermal drift issues

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The feedhorn / down converter on the dish has a pretty bad thermal drift issue. The output frequency is just not stable. It wanders around all over the place.
We have tried to settle it down by insulating it like thus;

It helps, but eh, its not the best way to do it as it does run hot, but it chops off about 10 Deg C of drift.
I think long term I might need some active temperature control, but that is only going to help so much. I think I need to see about a different feed horn.
Very disappointed.