One more comment , if you please---If you seal it up, haveplugs in each end,
and pressure test it before you fly it----If you prang it kinda hard one day
&
wonder if you cracked a weld--simply pressure it up-(nitrogen, argon,etc)
then see if it bleeds down----If it does, pressure it up with Freon, and go
sniffin with a leak detector. Saw back a few years ago where a guy left it
pressured up, and put a small gage in the ftg. ---one more thing to
preflight.

The CH7 (?) Angel homebuilt helicopter has a pressurized frame with gauge if
I'm not mistaken.

I'm kinda with Corky on the longevity of the tubing, but on my aircraft I
definitely like having raw linseed in the tubes to indicate frame cracks. That
stuff will leak out and leave a red indicator before the crack is noticeable to
the naked eye. It will also snitch on cracks under paint. That alone is worth
the oil to me. More than once it was the stitch in time that saved nine.