Thank you Walter D, the Sig kit is very simple and not-so-slow to build, but what really doubled the building time was those modifications. Well, I think it was worth the extra effort.

I even built a kind of "engine unit", I have a two-piece firewall and there is only 5 small hex bolts and after opening them I can remove the whole engine-tank-throttle servo unit for maintenance / bench testing / adjusting.

The trading brand of PETG sheet is "Vivak", it should be available in stores who sell plastics for industrial use etc.

More information about PETG "Vivak":

http://www.sheffieldplastics.com/product_vivak.cfm