trailer utility access doors 23 and 24 are provided in the sidewall 11 in order to render the joints of the various panels waterproof overlaps of the sheet metal are provided and include a top flange overlap 25 a front upper flange overlap 26 a front lower flange overlap 27 and rear flange overlaps 28 and 29 the metal skin of the sidewall provides bottom flange overlaps 30 31 and 32 referring to fig2 the right side or doorside frame 34 is shown comprising an upper frame member 35 lower frame members 36 37 and 38 front frame members 39 and 40 and rear frame members 41 and 42 additionally vertical frame members 1 2 3 4 5 6 7 and 8 connect the upper and lower frame members window frames and door frames are also formed by frame members not enumerated the various frame members are formed preferably of 7 8 inch tubular stock of rectangular cross section and preferably of aluminum to provide good strength at low weight referring to fig3 the top frame 44 is shown comprising a right channel member 45 and a left channel member 46 having a structure as shown in fig8 the frame is additionally comprised of transverse frame members 47 48 49 50 51 52 53 and 54 a light frame 55 is also provided as are other structures shown but not enumerated referring to fig4 the left or roadside frame 58 is shown comprising.