I was planning on building my own trailer. Lots of personal ideas, just like everyone else.

But yesterday, a "star" fell from the sky in the form of a one-year old, hardly used Harbour Freight trailer
FOR FREE!

It's the HD one with 12" wheels. Not wanting to kick a gift horse in the mouth, I accepted graciously. But I AM a little concerned about strength. I also wanted a 5' wide trailer.
Could anyone share their opinion on the best way to widen the trailer by 6" on each side, and would a torsion axel and 14" wheels be the way to go?