Proseal around aft firewall

So the instructions say to seal around the upper firewall after attaching the forward skin. Got that done with the remainder of a cartridge after closing the tanks. I can't find any referrence to the lower part of the firewall. Since mine is a QB I would have thought the lower would have been done while it was accessible. Either way it still needs to be done. A long nozzle extension is about the only way I can see getting PS behind the forward gussets.

I'd seal from the front side with 3M Fire Barrier 2000 silicone, but that's just me.

Take a look at the top of page 8-35.
My slow build RV-8 called for pro-seal between the firewall and skins prior to riveting the skins on. The upper firewall (above the bend line) gets done from the back side like you mentioned.
I would assume Vans completed that step with the quick build but a quick call can confirm it.

There is at the floor but the side skins up to the top forward skin is not. Daylight at every tab radius.

Rut Roh!!
It appears they decided to skip that step.
Makes me wonder what else they skipped.......

Try this stuff from AC Spruce with a nozzle extension -

http://www.aircraftspruce.com/catalog/cspages/al13064.php

No mixing and uses a standard caulk gun. I'm not sure if I would use it on a fuel tank, but it has all of the same sticky, gooey properties as the two part mix.