Looks like a fun project, I may build a Pico Lite this winter if I have time. If you go with a aluminium frame make sure you have the tongue strong enough. We have a aluminium frame for our dog trailer and the tongue started to crack after about 10,000 miles and it only weighs 250 lbs.
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I know this is old, but someone revived it.
Could the cracking be caused from being connected to a hitch that is non-sprung. Leaves the tongue to do a lot of hard bouncing.
Regards,
Don