What type of shotgun. How much are you looking at investing in this project? What gauge? I would look at Brileys for they make tubes for everyone and they are quality tubes.
Have them for all my shotguns from Mossbergs to my Kreighoff and Berretta. How experienced is your son at shooting trap? i would look at the Modified first and then maybe the Improved Modified after that are what I use for all my shooting from 16 to 25yd registered trap with 8's in warm weather and 9's in hot weather. After 25yd I go to Full and 7-1/2's for the extra energy.