What techniques are the best to make a gradually curved surface for the side of a model train? (photo attached) I would like some advice before I start a new build. I am trying to work out the best way of gradually curving the sides of a train as per the image below. The sides (on most trains these are typically flat) are slightly curved and feature windows inset into them which I will need to model. I was wondering what the best way to achieve this would be in Blender? Would a bevel work and if so then are there any tips that could help as I have found that beveling things to get coplicated if there are a significant number of curved surfaces. 

Any help would be very gratefully received. 

Thanks
Personally I would not use a modifier to do this, but block it out low poly at first. 

This was created (very fast) using extrude E, creating loop cuts ctrl+R then beveling these cuts Ctrl+B (using the mouse wheel to control the amount of bevel). 

Windows are created with Ctrl+I to insert faces, then F3 to repeat the same insert amount for all the windows.



the side curve are created with a single loop cut Ctrl+R, and scaled on the width and beveled it out Ctrl+B to get the rounding.