Not the least bit foolish Maxime, at least I don’t think so.

My pole was soaked in Tung Oil before she saw stepped and since then I
occasionally give her a quick coat just to spruce (pun partially
intended) her up.
I discounted using varnish for the reasons you mention but mainly
‘cause varnich is pain in the ass to get right and keep looking smart
whereas slapping on some wood oil is easy.
As for the chaff I’m afraid the parrels will eventually do that
whatever your mast is made of. There is plenty of good advice on chaff
prevention in PJR.
I have heard of junk riggers sheathing their masts with fibreglass and
epoxy to prevent chaff but me thinks that will cause more harm than
the varnish.
For my parrels I've used the slippest but softest rope I could find,
not that nylon stuff it too hard and will soon cut into the mast. So
far I haven’t had too much trouble with it cutting in. But I am
considering slipping some polythene tubing over some of the parrels.
By the way there is an excellent yahoo group for junkriggers. It
really is the best place for Junk Rig advice.

Mike.

http://timmynocky.terapad.com

I can't help but think that the pole would be more prone to rot if it
were varnished. Certainly it'll develop checks, so the rainwater would
get into it and get trapped under the varnish. I'd rather leave it
unfinished so that it can breathe. At most, if I see that the lines
are starting to chafe grooves into the mast, I'd give it a coat of oil-
based paint so that I could see the chafe spots and touch them up as
needed. I will abundantly tar the ends and use a masthead fitting to
cap the top.

Does this plan strike anyone as foolish?

Regards,
-Maxime