Fuel line through firewalls
Foremost makes bulkhead fittings in two sizes, standard and large. Standard size are color coded red and green and the large are blue and yellow. These are plastic fittings that secure with a nut on the backside of the fuse. I have used them with no problems. I also just run the lines thru holes and seal with silicone sealer - depends on the model.
The only thing about the bulkhead fittings is that if the front of your tank is very close to the bulkhead then there is not enough room for the fuel lines. The fittings protrude about 1/2 inch inside the firewall. If the tank is too close the the end of the fittings then the lines can/will have sharpe bends and kink.
I get my Foremost fittings at the LHS but I think they are (or were) available at Tower also. I think they are like $4.00 a pair or something.
My experience.
Dan