I can't really picture what you have or what you want to do. However, if its really short it will be very rough riding and won't handle the road well. If you want to mount a 5th wheel, you need to have the 5th wheel ahead of the drive axle and then have enough room to clear the cab. A headache rack will require more wheelbase and so will a winch. You need to decide what you want to build before you start building.