Well, call me a belt and suspenders sort of guy but I'd still like to see a bit of washout on a trainer. Especially if it's going to have ailerons. A bit of washout can make the difference in a turn when low and slow if the ailerons are used with a bit more gusto then they should have. It won't save the model from a gross mistake but it may let the pilot get away with a smaller one.

I'm guessing that the wing chord will be in the 10 inch wide range for a nice trainer like aspect ratio of 6:1. If so then about 3/8 inch of washout would be my suggestion.

It's normal to just warp it into the wing using the covering and the heat gun or iron to warp it in and hold it. If the wing uses a D box leading edge then shimming plus clamping or wdighting the building board to as much as it'll twist up to the max is also a good idea.