Many years ago when I bought my first gooseneck trailer with torsion axles, I was advised to purchase a tire changing ramp.  Looked at the local feed shop/tack store and in the tack supply catalog -- $65 to $100.  Gulp! 

We had just finished building a new deck on our house, and had lots of left over 2x10 pressure treated lumber scraps.  As I was stacking them up to carry them to the barn, I realized it resembled one of those expensive ramps that I was about to pay big bucks for.  So I broke out the trusty circular saw and cut the first 2x10 to 30 inches in length.  Cut the next one at 27 inches and nailed it on top of the first on (made one end flush, and the other staggered).  Continued doing this until I had built a ramp 6" high (a total of 4 boards nailed one on top of the next). 

That was 14 years ago, and I still use it today.  Since it is made out of pressure treated lumber, it has stood up very well to the elements (although I do store it in the trailer when not in use).  I have used it (1) to change a flat tire (2) as a scotch between the front and rear wheels when I unhook from the truck (3) as a platform under the trailer jack in wet/muddy conditions (since it has a surface area of 30" x 9 1/2" it will not sink in as much as the 8" x 8" surface of the jack's leg) (4) as a little mounting block for my extra-tall horse.

Now this thing is not exactly light when you try and move it around, but I also never had to worry that it would collapse under the weight of a fully loaded trailer as I was changing a tire, either.  And best of all it was essentially free to make.

There was a booth at the Nebraska Horse Expo this weekend selling the same thing....not sure what they were charging.  They had  drilled two holes in the wood and looped a rope through them for a  handle.

My trailer came with a metal one built in.  It forms the mounting block for the spare tire when stored on the trailer front wall.  Until last fall I had never used it on the road. But I do use it in the drive way at home to jack the trailer up so I can grease bearings, check the brakes etc.

As far as overloading the axle/tire. I think they can handle the weight, considering that you are not moving when you place the excess weight in them. There is no rotation or moments of energy being placed on the structure like would happen at 65 mph.