That´s not true. I´ve buit two trainers but the aim of my question was to learn the best way/technique/tools to build.

Anyway, I want to thank all of your advices/suggestions. I have learnt a lot with them.

One more question, by using T pins am I damaging the balsa?

For those who are also interested in tools here is a good thread
http://www.rcuniverse.com/forum/m_5189293/tm.htm