$fs=.25;$fa=1;
h=80;
b=40;
w=20;
rad=30;
wall=1;

rotate([90])
difference(){
  linear_extrude(w)hull(){
    translate([h-rad,b-rad/2])scale([1,.5])circle(rad);
    square([h-rad,b]);
    square([h,b-rad/2]);
  }
  translate(wall*[1,1,1])cube([h,b,w]-[0,0,2]*wall);
  for(x=[0:h/7],y=[0:b/6-x/8])translate([x*6,y*5]+(y%2?[3,0]:[0,0])+[5,4])rotate(30)cylinder(w*3,center=true,$fn=6,d=5);
}