form a splashboard an opening 42 is formed in the vertically arranged bottom wall 26a an l shaped connector 34 see fig3 is fixed to the opening 42 if desired such opening 42 may be formed in the horizontal upper side wall 26c of the channel member 26 referring to fig7 and 8 there is shown a fourth embodiment 100d of the present invention in this embodiment a depressed member 48 is mounted on the front side channel member 26 in a manner to define an enclosed chamber therebetween as is seen from fig8 the depressed chamber 48 comprises a major portion 48a disposed over the vertically arranged bottom wall 26a of the channel member 26 and a minor portion 48b disposed over the horizontally arranged lower side wall 26b of the channel member 26 an opening 50 is formed in a horizontally arranged lower side wall of the depressed member 48 similar to the afore mentioned embodiments a depressed side edge portion 36a of the front under cover 36 is spaced from the opening 32 to form a splashboard an opening 52 is formed in a top wall of the depressed member 48 for connecting with the l shaped connector 34 if desired such opening.