Intake sealing and blocking the heat crossover

I did some forum searches and read several threads but I still have a few specific questions about intake sealing and blocking the heat crossover. The engine is a stock rebuild 360 and I'm putting on an Edelbrock performer intake. For several reasons including how I live in a warm climate I want to block the heat crossover.

From what I gathered sometimes, or often, the gaskets that block it off burn through. Several people on here say they cut a piece of shim stock to assist the gasket blocking the port. I have a few questions about that.

1. Will the thickness of the sheet metal interfere with the intake sealing?? Will it crack the intake if bolted down? Do you guys cut or modify the gaskets to compensate for the extra thickness of the added block off piece?
2. I have .008" stainless steel shim stock, is that thick enough? Or should I order some thicker?
3. How big of a piece should I cut to block the port? Any pics/advice appreciated. I want it to stay in place and not fall in or shift.

Also, which gaskets are you guys using for a build like this? Iron heads and aluminum intake. I read the Felpro printoseal gaskets seem to be popular? Is there a better option for my application? I also read there's Mopar gasket set that come with block off plates but I was unable to find that, and I also want to know if that's a good option. I definitely want gaskets that seal well and are reliable.

Lastly I noticed several people saying to discard the end gaskets and just use a bead of high temp RTV. What's the reason for this? Why not just use the end gaskets and coat both sides in RTV? Are they too thick or something?