Firewalls are a pain as they are not made to come apart
. Whichever you choose.. keep in mind the little tihngs like making holes for fuel lines... maybe needing longer bolts if your doubling up the firewall.. geting the blind nuts out ofthe original, etc. For thinning epoxy... I just pass my covering gun over it.. turns to a runny syrup and flows in all the nooks and crannies... i often brush it in as well.. but will also kick off faster due to the heat. But this way there's no thinning or add'l mixing needed.
Good to see you fixing.. once you get in there... it's not really that big a deal... the next one goes faster.. and the one after that even faster
In our club... one guy tore his landing gear out and was goingto buy a whole new fuselage... craszy.... so i fixed it for him.