Fittings onto fuel lines install HELP

Hey, for all of you with upgraded fuel lines and stuff, how did you install the fittings onto the fuel lines? I have -08 fittings and hoses (along with -06 for the return lines) and have tried EVERYTHING i could possibly think of to try and slide the fitting onto the fuel line. I tried a heat gun, assembly lube, wd-40, my strength.. nothing seems to work.

Any help with this odd question would be greatly appreciated.

I'm trying to install the fittings that need to be attached into the fuel lines so that i can connect the fuel lines to the fuel hat, filter, regulator, and rails.. Fuel Hat to fuel filter, then to the passenger side fuel rail, then to the driver side fuel rail, then to the regulator, then from the regulator back to the fuel hat as the return line.

Fragola -8an 120 Degree Stainless Race Hose End [FPS-112008] : Lethal Performance, Performance parts for Ford Mustangs

those type of fittings, but some are straight, 90 degree, etc.