Rear bed wood questions

[Bullett]

O.k., I stained up my wood today that I will be using for the bed in my truck. I had access to some torque and groove 7" pine boards and I have some 1 1/2" s/s strips that came with my truck. I am trying to do this on a budget. I have $30 in the boards. I am going to cut the toungue and grooves off the boards, I am then going to put the perimeter boards in the body and fasten to the bed with carriage bolts. The rest of the boards, I am going to get them spaced where I want them and then I will have a couple pressure treated 2"x2" ties on the underside, I will screw the pine boards, on the very edge of the boards, to the ties underneath and then I will hide the screws with the s/s straps. I am not experienced with wood work but how much space do I want between my boards? Are the boards going to eventually shrink? Lengthways or width or both? I will have the 6 carriage bolts showing that fastens the wood to the body. Why are the carriage bolt washers, that hold the bed down, that come in the bed wood kits, they seem to look like their drilled off center?



Hope this makes sense, I am late to a bday party. Hee hee.