Firewall Doublers

Do I need to use products such as 3M Fire Barrier 2000+ when I install doublers on the firewall? If so, do I put it all over the doubler, rivet holes, or only where items pass through? An example is the doubler plate used for the brake line bulkhead fittings on the 7 I am building.

Most people use a fire sealant over the grommet and/or wire penetrations, but not over metal parts per se. Some people get steel bulkhead tubing fittings instead of the aluminum ones provided in the kit, but there are mixed reviews on this.

I'm interested in this thread because in the not-too-distant future I'm going to do a panel upgrade. When I do that, the TruTrak Engine Data Module will be replaced. There is a hole in the firewall to allow plugging in the plugs from the engine side of the firewall into the module.

The next system I have will almost certainly NOT require the same size/shape hole. What is done in the case where the new hole is not the same shape as the old..maybe bigger in one direction and smaller in the other....

Is it good practice to cover the hole with a stainless cover plate that's also sealed?

If I understand your question, yes, it's a good practice. Search on Aircraft Spruce (or your favorite other supply) for firewall shields.