notch for 97 FS

well i am going to have a notch built out of square tubing, but before i can, i need messurements and find out how thick the wall needs to be...i was told to go with 2x3 but how thick should the wall be? is 1/4 too thick? and also, does anyone know how long each peice should be? i figure an 8 inch notch should be sufficent to lay frame. any help on this matter is appreciated.

do a 10 in notch,then when u want to put bigger wheels,it wall still lay