Just a word of caution, you many end up needing a CDL and possible different weight registration on the truck. you may want to call in and see or do an online search in your state to see what you can legally haul, they have been hammering contractors for some years now, with the over 10,000 pound limit, on the tuck, hauling supplies and small bobcats and so on,
most likely your trailer is rated for 21,000 pounds, possibly more, depending on how they figure tougne weight,
and there is a good chance you may need a DOT number as well, from WA state.
http://www.wsp.wa.gov/traveler/docs/cvd/DOT_Requirements_for_Commercial_Vehicles.pdf
If you have farm plates or agricultural exemption, you may be OK. depending on how the rules in your state read, I have heard some horror stories on the fines some have got,
Just some thing to consider.
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on the deck you may need some more cross bracing if it was original wood,
when my son and I rebuilt mine, we double up the cross bracing, most likely could have used, lighter than the 3" channel but it was the same as the other, but to use 2inch would have resulted in having to shim each one at eh frame,
my Idea was to put down a few channels under the tire area, and fill back in with wood, but since my son was hauling scrap iron at the time and keep dumping and dropping tings and breaking up the wood, we ended up with flat metal decking (eh found some 1/4" and it held up to his scrap iron, but he was hard on that trailer,
for ever pound of trailer you have is that much less before the trailer is over loaded,
at one time all they cared about was weight per axel, now it is the tires and the rating on the trailer, if what your hauling is over manufactures tag or the tires tag on the side wall, , your over loaded, some thing more to consider,