As my first RC instructor told me, it's your plane, you can do what you want with it!!
As builders most of us just use rolled up bond paper. I wrap mine around a 1/2 inch dowel then tape it, after it is inside the wing I use CA and glue them in.
!/2 inch rocket tubes will work just fine, just a bit of unwanted weight. If it's a problem you can always buy a bigger engine!![8D]