Max length can depend on how robust the front end of the receiver is.
I once had a 450 footer - my R-71a ate it for lunch. The same antenna
blew the brains out of a Sony 2010. (Live and learn. Fortunately the
2010 was under warranty and the Sony repair depot was 4 miles away.)

Years later I had another good one - a 240 footer at about 55 ft high,
going to a Drake R8a and a Yahoo Frog-A-Hunnert.

For your situation .. experiment. My experience is the longer (and
higher) the better. And with the Tun-4 you should be able to tame it
down / tweak it up as needed.

For handling the "higher is better" part - a fishing reel bolted to a
wrist-rocket slingshot with hose clamps is 2nd best. A poor man's E-Z
Hang, if you will. Hey E-Z Hang was on sale at Dayton Hamvention for
$90.00 or so. But for about $20.00 and a trip to the Wal-Mart sporting
goods department, you can make one that works fine.

First best - an archery fishing reel attached to a good hunting bow.
Awesome results if you're a decent archer.

Ok .. the *real* first best is a Lyle gun and a few thousand feet of
rope - but this might be overkill. :-)