Installing a door in the wall for under floor crawl space

The previous owners installed gas ducted heating through the access hole in the side of the house to get under the floor. I'm removing the heater and the ducting, with plans to put underfloor polyester insulation or foam board, or both.

I need to build a new door and frame in the hole in the brick wall. The hole is about 700x600mm. Are there any particular designs that allow a tight fitting door to keep bugs and rodents out, as well as being a minimal design so it doesn't make the hole too much smaller?

Also, should the door be flush with the wall, or set back to give it some rain protection? I'd really like to use lift off hinges because the access hole is in a tight corner, which I don't think I can do if the door is set back.

Thanks