insideheight=17;
insidelen=41;
insidedepth=22;

wallthickness=2;

screwboxlen=10;
screwboxheight=5;

cablecutdepth=17;
cablecutheight=5;
cablecutz=3;

difference()
 {
     cube([insidelen+2*wallthickness,insidedepth+wallthickness,insideheight+wallthickness]);
     
     translate([wallthickness,-wallthickness,wallthickness])
        cube([insidelen,insidedepth+wallthickness,insideheight+wallthickness]);
     
     #translate([insidelen+1*wallthickness,-wallthickness,wallthickness+cablecutz])
        cube([wallthickness*4,cablecutdepth+wallthickness,cablecutheight]);
 }  
 
 translate([-screwboxlen,0,insideheight-screwboxheight+wallthickness])
        cube([screwboxlen,insidedepth+wallthickness,screwboxheight]);
 
 translate([insidelen+2*wallthickness,0,insideheight-screwboxheight+wallthickness])
        cube([screwboxlen,insidedepth+wallthickness,screwboxheight]);