Could you? Would you?

[Jack]

Square or rectangular tube, it's easier to weld/attach panels, etc.
Ususally heavier than required for convience.

Round tube sometimes used in greater section than square for extra modulus at equal weights. Real pain to attach panels unless "wrapped $ rivited".

Have built both ways, square is much easier.

 

[Fred W Ballinger]

I plan to use a combination, square where panels will attach and round where you can see it when the body panels are open

Reagards

Fred W B

 

[Chris Kouba]

Disclaimer: I have not built a tube frame anything.

I would wager round comes into play when there is a tubing bender involved. As already noted (but I will repeat anyway), I have also heard that square is a winner when there are panels to attach.

That's not to say you can't bend square or panel up round, just way more convenient.

Chris