what size fuel line for nitrous setup?

Assuming that I did the math right the difference in weight of fuel between a full 3/8" tube and a full 1/2" tube over a 15' length is .067 lbs.

Since drag racing appears to be the plan I'd go with the 1/2" tube.

I make brackets for bulkhead union AN fittings at each end of the fuel tube. That gives a secure end to the tube and a good way to make the transition from tube to hose.

If you use the aluminum tubing make sure to use an Adel clamp every 18" at most, and give the tube a little excess length in the form of an subtle S curve at each end if at all possible. Aluminum's thermal expansion is quite a bit larger than steel's. Adding the S curves allows it to grow and shrink w/o putting undue stress on it.