Hi Mike, here's a version saved off but it still needs more work to clean up the juncture areas where fillet pieces meet up.

These fillets were put in by doing a lower level surface/surface filleting - that's where you use Edit > Separate to break the model up into individual separate surfaces, and then select 2 of those surfaces at a time and then run Fillet. That can construct fillet segments for situations where the edge-based one can't figure out juncture areas. But it means the junctures have to be manually created by trimming and construction of some fill in pieces yourself.

I also used loft for some pieces to build a larger piece from one side across to the other to get rid of the additional edges running down the middle.

I'm still not entirely sure if this is actually the area that you wanted smoothing in or not.

There are some changes you could make to the body structure that would probably help with filleting - if the 2 roof top pieces that are at very slight angles to one another were instead made up of one large slightly curved surface instead that's probably better for filleting for example.

The least amount of fragmentation as far as number of edges and faces tends to be helpful.

- Michael