I'd go with the semetrical door hatches. That would seem to make sense from a "40k life" structure point of view. As for worrying about stairs, why not just add one or two access doors to a rear wall and be done with the whole thing? that way you give the idea that there is access to the rear part of the flyer, but don't elude as to how it is actually reached.
Is there any chance of a scale shot so that we can look at how it compares to the models that it will likely be carrying. Of course, the rules for the THawk tell us the capacity and whilst we all know that 40K vehicles are scaled slightly differently to the infantry it would be good to check that you are in the generally correct area.
Also, instead of a rear hatch, why not a belly hatch underneath the rear portion - before the engines? That would seem like a good spot for stowage, or maintenance access to the engines and main gun.
The other thing that needs to be considered is how the finished model will "stand". Are you going to give it a flying base of sorts, and if so, how are you going to achieve this securely. I ask now, because I imagine that preparations may have to be made for any stand (depending on the design of stand you settle on).