My trike uses kingpins I made for tapered roller bearings. I cant remove either bearing as they need to be locked against each other to work. I included a picture of the kingpins assemblies I machined, they obviously have all the rest of the steering hardware welded to them now.
The steel I used for this is 50mm square box section with a 3mm wall. The actual frame is not hugely weighty, the wheels double the initial frame weight I would of thought.
There was an upgrade package for the kmx trike seat. I bought it, and made it fit my trike. I decided I didn't like it, although it was comfortable it certainly was not weather proof. I decided to make a bucket sort of seat which comes out the frame using 40mm x 3mm flat bar. Will add weather proof padding where necessary. The only bit of padding I feel I need is on the rear shock support for my back. The rest feels really comfortable for me, and keeps me in one place without risk of falling out in a corner. Others who have tried preferred the kmx seat, guess this happens when you make it fit one person
Few pictures of where I at.