I've been fishing 4 inch tubes in a, uh, let's call it "experimental" fashion lately.
I've been putting a 1/8 egg sinker all the way in there, then sealing it it up with a chunk of senko (lube up a discarded 4" senko with megastrike, then push it all the way in. Cut the senko flush to the opening in the tube). Then I rig it backwards like you would a fat ika, but with a 1/0 EWG.
It has a different action than an ika or a tube - it's pretty neat and the fish love it. It will sink slower than expected and it wiggles back and forth on a steady retrieve. It's also pretty darn weedless if you skin hook it.
It's not without it's problems, though. You pretty much need some kind of fish attractant to lube the senko chunk, otherwise it's just too d**n hard to squeeze in there. Also, it's annoying to get the hook rigged up properly. Even worse, it's tougher to get a hook up on this rig than most others - they'll bite it all day long but the hook doesn't always want to set.
A different kind of hook may help there... I just use the 1/0 EWG because it's short enough to not intrude on the egg sinker and it's weedless.
Anyway, it's goofy and a lot of guys might find it more hassle than it's worth, but it's a fun way for me to fish something that generally collects dust otherwise.