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A few thoughts on trailer design.
  1. Gross trailer weight + cargo + fuel + fat chicks should be no more than 80% the weight rating of the axle - personal rule of thumb. Forces me to build stronger trailers than what I'm hauling.
  2. 10-15% of your total trailer weight should be on the tow rig's hitch (3000lb trailer * 10% = 300lbs tongue weight)
  3. Strength of a trailer frame initially comes from how tall your I-beam or C-channel is, with consideration to the material thickness. Better to have a 2" C-channel or I-beam than a 2x2" .120 wall square tube. The trailer's rigidity will come from how you make your crossmembers and what portions you box in/use tube.
  4. A-frame designs are usually stronger designs than monobeams
  5. Most states require trailer brakes on at least 1 axle for trailers rated for over 3000lbs...yours might be over that, especially when full of fuel, camping gear, fire wood, ect.
  6. Rule of thumb axle placement should be at a 60/40 split plus or minus a few inches. If you have a 10ft long trailer overall, put the axle 6ft back. This helps to ensure you have enough tongue weight.

With that said, I just got done building what you're basically aiming for.. a trailer you can tow behind your Jeep with ground clearance to handle the same trails. Your 12 bolt has a GAWR of 3750lbs give or take, so add up the weight of your trailer frame, fuel & tank, supplies, leaf springs, battery?, and everything else and you might be able to have a 2000lb haul trailer. I used two sets of leaf springs from a late 90's Tahoe. 54" long, centered pin and they're relatively cheap. I used two main leafs, two #2's, two #3's and did not use the overload. So far I've hauled a 3/4 cord of wood four times with it, two heavy motorcycles once, a set of 1-ton axles once and $1500 dollars worth of roll cage tubing twice. So far I can't complain. If you're going to use the J20 springs, plan on slipping another leaf in to support the main leaf. You'll lose inches of tire clearance within the first 200lbs. Stiffen up the main leaf somehow.

For materials I used 2x3" .250 wall for my draw bar, braced with 3" C-channel to the leaf spring mounts in an A-frame fashion. The rest of the trailer is 2.5" angle iron .188 wall with 1.5" .125 wall angle iron railings. If you use 3" or 4" C-channel for the frame rails you could probably mount the J20 box easily in a factory fashion.

Shocks I used S10 4wd front shocks. They're short, but have plenty of dampening pressure for when I'm loaded down. Cheap too.

If you don't want trailer brakes, keep the weight down. Keep in mind a typical cord of wood weighs 2500-3500lbs depending on species and how dry it is. Weight adds up fast.

Put more tie down points than you think you'll need. You'll end up using every one of them. I have them spaced every 2ft, with additional tie down points up front and in the corners.

I don't want to clog up your thread with unwanted pictures, so PM me if you want to see what I built.
 
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