What size and how?

So, after reviewing quite a few designs and thinking of a few on my own I have decided on a traditional tear. My question is how large of a tear does everyone have. I see a lot of 5x8's and I want to know if I can extend a harbor freight trailer to make one. I'm thinking of just cutting and welding in a 12" piece of angle iron in the center of each section. I guess I would have to extend the axle too. What thoughts or expierences does everyone have... and Is a 4x8 way to small. Thank's Wil