Be carefull with thrust angle and thrust line height. Can be confused . A boomerang has the thrust line very close to the (vertical)Cg , changing its angle a little don´t change its height a lot with respect to the Cg ,that´s what really counts.
Ask a harpoonII owner how easy is to get into problems with thrust trim .... I have seen it flip on take off.
Some cheap ducts can suffer from heat but normally thre is no problem,a lot of fresh air is bypassed into the duct.