Another way for a consistent surface to work with could be, and I haven't done it before, but I've read about it. There's a method of cutting up the sprue from the same kit, and mixing it up with styrene glue which will form a thick plastic liquid., and you can work it how you want. This would be a huge amount of sanding, but wouldn't shrink over time, and would be a consistent surface to rivet and rescribe in.
I've done this before and it makes a great, very sticky and very strong substance that holds parts together well. One downside is that it can become very stringy like the old Testors tube glue.
If you have trouble with seams popping when you are sanding, start gluing wings and bodies together with this glue and styrene mixture. The other downside to this stuff is that it takes a fair bit of time to completely cure. If I use it, I don't touch the model for over a week.