Ray Peters built a small enclosed one bike trailer aerodyne (stealth style)using a brief metal structure and a corrugated plastic sign material for the panels. Tied together by ty-wraps, weighed nothing.

It works!

The side of a box trailer are usually ribbed for extra.... strength If you have a commercial vehicle scrap dealer nearby I'd try them as the side of an old box van or artic trailer are ideal and very cheap to get big sections of.

i'd like to take that further

1 transit write off cut at bulk head weld on large flat plate,

2 weld angle iron supports for hitch,

3 fill holes with expansion foam and paint with gloss emulsion on a roller,

4 wire lights to socket,

Done...