For my next question. How many SD members actually own a cordless drill
Sadly about a dozon of them in various states of repair / function
Building the seat is streight forward enough asuming you have some basic carpentry skills but geting the ergonomics right is a little harder
Criticle dimensions are
Seat height to gun rail
Seat distance from gun rail
Seat height and distance from foot rest

Seats without a foot rest are uncomfortable for long sits. Seats with the wrong ergonomics for the gun rail are just a pain
I am a building surveyour and ex engeneer so not too bad at the design side but my first attempt made some of the above errors. Second attempt was much better
I put the design up on the web site
http://www.dagse.co.uk/resources/free-standing-high-seat-design/
The gun rail is purposfulley a little on the low side. But you can simply add lengths of 4X2 or 4X4 to raise it up to the corect height for you
Lowering it would have been MUCH harder
As for getting it in a car? Dont bother get a trailer
NOW if you mean a portable one thats colapsable and fits in a car? Then buy a telescopic high seat and a simila height telescopic ladder
Then use the telescopic seat as the seat an use the ladder to create an A frame at the back. Then all you need is guy roaps to make it stable