I have used Silicone in the past...but found it to be heavy...when compared with epoxy. For the Firewall I use Epoxy actually Zpoxy finishing resin...and mix it with micro balloons until it is a paste....

I then use my finger and make a nice fillet front and back of the firewall....and use a small piece of balsa with the corner sanded round or at an angle like 1/8" corner...maybe 3/16"...then scrape all excess resin off and it will give a perfect and clean joint without any excess resin...

For the Nomex plates and formers I use epoxy in the tail end but up front like on my Smaragds and Hydeaway kits I have used Foam safe CA to secure the nomex trays...also the epoxy and micro balloons works very well in the this situation also...Just put lots on and get good coverage then scrape it all off except a very thin fillet at the joint..Works good every time and they don't come loose.
I just test flew my 5th ZN line kit before Christmas a Hydeaway and this works every time.

Zap a Dap stuff will melt the foam....and its heavier than Silicone! the epoxy if you clean off all the excess is very light..the foam safe CA is even lighter....Firewalls, and tail formers should always be glued using epoxy....Pro-bond makes an ugly and non consistent surface and silicone type adhesives are just too heavy...


Years ago I compared the weight added by using silicone and the weight added by using just epoxy on two separate planes...weighed before firewall install and after firewall install the result was the silicone was almost double the weight.....If you sand the inside of the fuse the epoxy works just as well holding things....the silicone tends to have a better grip on the inside of the fuse....be careful though some planes like the Piorin kits are not epoxy glass and I think the silicone will reach with the resin....

Not positive here but.....I know the resin henry uses is more like a polyester type than a Epoxy type....

Troy