If your building a trailer, I've got a little tip for you. One of the things I've added to all our trailers is a second axel, even if it doesn't need it for the weight. Having that second axel adds a lot of safety if a tire blows on a loaded trailer. I've had tire blow-outs on four-place snowmobile trailers with only one axel and it was scary and dangerous. The second axel helps out a lot. I even prefer it to a single axel/dually setup, as it gets better traction in bad weather.

TY for the advise. I've blown single axle tires before, and if you aren't expecting it, it can be interesting.

For now, I'm sticking with the single axle, and GOOD tires, for several reasons.
I often pull single axle, and 2 axle trailers, at least once a week. Even though I'm going to be under the weight requirement, I will have breaks at all wheels.

Single axle are not that bad if you are driving within your and the trailers limits.

That's the key, know the limits of the trailer, and tow vehicle. All my hitches are 2-5/8" Bulldog hitches, and I use torsion bars, and anti-sway bars if needed. All my trailers, even those under the weight limit, have electric breaks, and full breakaways. I buy the best tires I can, and check them regularly on tow trips.

What you want is something like this:

http://www.adventuretrailers.com/

No I don't. Building a hard sided trailer.

If I was going offroad for any length of time, I'd chose a Unicat.

Built on a Unimog chassis, as used by European armies.

It's available in the US if you've got the $$$, and there's not much that would get in your way in one of these!