whynotfab
+1y
1/4" port would still be quick on the rear of a truck.. I know I have 1/2" port contitech 2600s, and 1/2" SMCs on the tank, but use mini-ball valves and reduce it down to I'm sure closer to the 1/4" size (or smaller actually) and I'm happy with it.
Just be sure to use DOT approved fittings, I used to have 1/4" port firestone 2500s on the front of my truck.. and recently switched to 1/2" port contitech 2500s and don't really see much of a difference.. the fittings had about the same size ID it seems anyway..just run 1/2" line.