I’ve spent lots of time trying to find a utility trailer that could be easily converted to work.  It would eliminate lots of the metal fabrication and simplify the title and registration.  Here are some of the trailers I have looked at:

Harbor Freight 1720 lb. Capacity 48 in. x 96 in. Super Duty Folding Trailer ($400)

Ironton Heavy-Duty Trailer Kit – 5ft. x 8ft  ($490)

Carry-On Trailer 5-ft x 8-ft Wire Mesh Utility Trailer with Gate ($700)

Challenges to using these trailers include:

• Very small wheels that have a low speed rating.
• No flange to mount electronic brakes if desired
• The metal is as thin and light as possible which doesn’t leave much room for modification
• The axle location will need to be moved when the trailer is lengthened to get the correct tongue weight so that it will tow well.

So for this set of plans, I recommend that you start with fresh steel and an axle sized to your specification.    Yes. It is more expensive but you get a higher quality product.  A trailer that is much sturdier and road worthy than any of the utility trailers.   But if your fabrication skills are up to the task, there is no reason that a donor trailer couldn’t be used.  I’ve covered the calculations for making sure your frame is strong enough in another section.  So deviate at your own risk.  Just make sure that your frame and tongue are sized for the load and that you get your axle placed in a position so that it is easy to load the trailer correctly.  I’ve written about that too in another section.

If you are uncomfortable welding the frame, I’d suggest you get a quote from a local shop and see how much they would charge you to build one.