Do you already have a trainer that you are flying? If no, I'd say putting the Tower Trainer together (with or without modifications) and flying it for a while is a really good idea.

If you have already bought the trainer, modify at will. I'd put the total dihedral at 1 or 2 inches, mostly because I think trainers look better with some dihedral.

I have a Great Planes PT-60, built as tail dragger, with zero dihedral and dual aileron servos with much more travel than stock. I also had one with the 4" dihedral 'Sport Wing' and no modifications so I have direct comparison of the same kit with and without modifications. Even though the modified version rolls a little better, and you have to deliberately level the wings after a turn, it is still a trainer. With the exception of crosswind handling I see very little difference in the stock versus modified versions.

If you have not spent money yet, and you have a trainer to fly for a while, you might consider an intermediate plane rather than a modified trainer.

There are several planes in the $100 to $120 price range that I would choose over a modified trainer. I do not know if you want an ARF or a kit but all of these are 40 size ARFs.

World Models Sky Raider Mach II http://ecsvr.com/abm/shopexd.asp?id=2926
World Models LA Racer http://ecsvr.com/abm/shopexd.asp?id=2140

Tower Kaos 40 http://www3.omnimodels.com/cgi-bin/w...I=TOWA2052&P=0
Great Planes Dazzler http://www3.omnimodels.com/cgi-bin/w...I=GPMA1038&P=0
Phoenix Dolphin http://www3.omnimodels.com/cgi-bin/w...I=PMMA0250&P=0

Carrell