this post has a picture of what happens when you lose one wheel on a two axle trailer.http://cpyoa.geekworkshosting.com/forum/index.php?topic=7745.msg56979#msg56979
If you have a flat, or take off the wheel, the spring will force the axle down until it or the brake backing plate drags on the road.
The solution is to carry a short (3-4') piece of chain and some quick links.
Put the jack under the axle by the missing wheel. Jack up on the axle as high as you can get it, to the point you're taking all the weight off the other tire and onto the jack.
this compresses the spring, as all the weight is on it.
Carefully (make sure your jack is on solid footing) wrap the chain under the axle and around the frame, connect it with a quick link as short/tight as you can.
Now lower the jack.
The chain is now holding the axle up, tied up to the frame, and the axle or backing plate won't drag on the road. ...although it might be close.
Carefully and slowly proceed to where you can make permanent repairs.
1.Be careful with chuckholes, obstructions, and etc, because it could be easy to catch the brake backing plate on things and tear it up. Its hanging out there unprotected. You could take it and the brakes off if you want to get more road clearance. Don't let your trailer be bouncing up and down or it will scrape.
2. if this is the brake axle and you lose the hub (assuming drum brakes) you have no brakes. If you take off the hub/drum, you have no brakes. Even if you have the brakes and hub intact, you have no tire and thus no brake on THAT SIDE. but you could on the other side, so when you brake the trailer can pull to one side, so be very careful when braking. If your problem is a blown tire and not a wheel bearing, move the good tire to the brake axle and chain up the one with no brake, which is usually the following (rearmost) axle.
2. You now have the weight on that side of the trailer riding on one tire instead of sharing it between two tires. So that second tire had better be in good shape. Be careful not to hit anything, make sure the tire pressure is correct, and drive slower so that it will stay cool. It's quite possible you could be overloading and damaging this tire if it's not rated for half the weight of the load.
I've used this method twice. The first time I had a bearing go out, about 2 miles from home. Chaining up the axle got me off the road and to my house where I could fix it.
The second time had a bearing fail on Sunday afternoon in the middle of nowhere, the wheel actually came off, and I didn't want to leave my boat setting alongside the road. I was about 1000 miles from home,. I drove over 150 miles to my destination on the interstate at around 50mph with a chained up axle and a good tire on the 2nd axle, no problems. I was just careful to watch for chuckholes, planned ahead for braking, and drove relatively slowly.