The man said he wants to fabricate a trailer, and I take that as make and not modify so I say get the tools and materials out and go for it.

I favour the seat hitch point over the left hand triangle every time, and I also favour 20" wheels for trailers.

I have no idea what capacity of volume or payload you require, and although I build and sell more two wheel trailers than single wheel trailers my personal choice would be a single wheel trailer and if you are going to fabricate one then why not make it a good one and I really do like these single wheel