6 minute epoxy will not give you enough working time.

You want 30 minute epoxy.

Mix up the epoxy FIRST, then once the mix is smooth, add a bit of alcohol or acetone.

I prefer alcohol since it will not attack covering or paint.

Mix everything until you are left with a runny syrupy mixture.

Use a brush to cover all exposed firewall wood, and anything that is left over use on exposed inner surfaces, particularly wood joints, to add a bit of strength.

As ChuckW mentioned the Stik already has fuel proofing, but a bit more will not hurt.