the tunnel heat issue is resolved easily by:
1) putting some sort of insulation between the heat valves and firewall. Best would be a piece of silicone baffle material - this largely prevents the heat blowing on the valves from conducting to the cabin side (tunnel) and therefore heating up the tunnel
and 2) swapping to the stainless heat valves which have much better sealing than the stock aluminum versions.
If you elect to stay with the stock aluminum heat valves you can get probably fix most of the issue with generous application of red RTV in strategic locations on the valves. First, air gets under the hinged side of the flapper because of the play in the hinges. Make a little RTV air dam so the air isn't blowing directly on the hinged edge of the flapper. You might also consider a light coating so the flapper seals better when shut. You can see the issue by simply hooking up the blower port on a shop vac to the engine side heat valve air port and watching what happens.