(zbrush -zmodeler) piece of cannon

Falkenbach80

hi, i'm a newbie with zmodeler, and i'm trying to make a predator tank from warhammer 40k
i'm tryng to make this "hider" (red circle) but i've not ideas how make the rectangular substracts from the cylindric shape

can you give me some hints?

if i add edges to the shape for make the hole more "creased" the circular shape become deformed (as shown)
Thanks and sry for my english

musashidan

Uncrease the edges running across and around the cylinder and only crease the edges around the cutouts where you want a hard edge.

Falkenbach80

thanks!