I'm thinking about building a utility trailer out of aluminum for my ranger and other shit. have built several 5x10 even a few 6x20 but all were out of steel. Anyone ever build a trailer out of aluminum, say 4" channel like my boat trailer?

I had the same intentions. By the time I priced it all out, I was close enough in cost to just search for a used alum trailer. I found a used Aluma brand for about $400 more than the cost of building. I wanted side and rear ramps to haul an ATV and side by side. If your needs are not as specific, you may be able to build cheaper than I could. Look into Semi trailer alum cross members and side rails. If you look around you should be able to find sections of rails that will suit your needs. Find a Utility or Great Dane trailer shop in your area. Both use Alum cross members for their reefer trailers. In many cases rails are not completely replaced leaving plenty of scrap pieces that can easily be well into the 16/18' lengths. They can be hucked together using factory holes. Gives you a nice clean look. And that style cross members will allow you to secure various deck materials when you decide what you want. Torsion axles are easy to come by and easy to install. That's what I was going to use due to the ease of install.

Yeah I definitely was going to do the torsion axles, gonn ahev to look into that other stuff you mentioned.

The cross members I mentioned are built to support a forklift and load. Keep that in mind when considering spacing. Depending on deck material you chose of course. I was planning on a 24" spacing with Aluminum diamond plate. They are an I beam style cross member. They also have plenty of room to drill and use grommets to run wires for lighting in the center of them. Or even drill to fit conduit and run wiring enclosed. Time consuming, but well worth it.

I buy a good bit of material from the local steel shop who also carries aluminum. I'll probably built the main frame out of 6" 1/4 wall channel and the cross members out of 4" 1/4 wall. 6" is what I built my boat trailer out of. Also looking into torsion axles so I don't have to worry about the damn springs and hangers. Just waiting to hear back on the price on the channel.