I built one with a 3,500 lb axle also. Here are a few of the lessons learned/unsolicited suggestions.
1. order your axle to match your jeep tire width.
2. use the same size tires as your pull jeep.
3. buy fenders that meet your state legal requirements, building from scratch is a pain.
4. decide everything you need it to haul and build it to 10% bigger.
5. I use the Military style towing pintle, cheap and effective. Butit is noisey and is harder to back up when it is offroad.
6. Make sure you can build it to your states registration and title requirements. And your willing to do that extra work.
7. Design it to protect the lights, wiring and that it wont get snagged on rocks..
8. make the base frame stout if you are dragging over rockes, the upper frame supports can be lighter.
9. put drain plugs/holes in it.
10. Design it and put it on paper. Let all your friends look at it and get their input. Try to build it right the first time, changing your mind can get expensive. You can always add things to a well built trailer.
11. Put a roof top tent on it if you plan on camping, trust me, they are awesome.
I have about $2,000 in mine minus the Tent. My BIL (engineer type) has about $5,000 in his, but it is awesome.
All of this is excellent advice...I'll add a little to it..
1. Absolutely...mine is the same width as the jeep, therefore, it'll go where the jeep goes. I did a #1500 to start with. On the first trip out I put a side load on it on both sides. By this I mean as I went over a large rock with one tire the loaded trailer had a lot of weight on the opposite side. This resulted in the spindle bending. Picture an old swing axle VW beetle. After replacing with a #3500 there have been no more issues.
2. Yep..and bolt pattern too. You can get the trailer hubs in 5x4.5. I used 33x10.50x15 BFG ATs.
3. I bought the fenders at TSC and trimed a few inches off each end.
4. I had a size in mind when I did mine. It came out t 44x68. Has a fold town tail gate too.
5. Look at my pics for the hitch. I used a receiver and have multiple hitch options. Pintle, ball, farm implement. Depends on what I'm using it for at that particuliar time.
6. Not too difficult to do at all.
7. I used oval LED tails and all wiring is routed to avoid any snags etc.
8. Yes. My main frame rails are 2x4 rectangular tubing. All other tubing is 1/8 wall 1 3/4 square. Inside panels are 1/8 sheet and Rhino lined.
9. Drain holes make clean up much easier.
10. Ideas from friends are always good when planning.