There are a few different ways to smooth out foam. I'm not going to use a hot wire but I'll show you that anyway. I put two pieces of welding filler rod into a soldering gun and strung some .023 MIG wire between the two. Pull the trigger and the wire gets hot enough to cut. The benefit to this method is that it's very clean. No dust at all. BUT, although you can get pretty good result, you'll still need to sand to smooth the form out. Also it's somewhat slower than full attack mode with a grinder.
Here's a picture of some cuts made by hot wire. Notice there are no snow drifts left behind.
My preferred arsenal for this size job consists of a razor knife, hack saw blade, mud rasp, and a grinder.
I have smoothed out the 7 center layers that are permanent. Then I cut out the removable inboard and outboard parts.
I cut out and glued the removable parts and smoothed them out. After I finish making the left liner, I'll take these off and make new ones for the opposite side. Much easier than making two complete forms.
I've reconsidered using a sheet to draw the ABS down. I wouldn't be able to reheat if I have to. I think what I'll do instead is use strips of fiberglass screen about 8" wide. If the ABS starts cooling before I get it fully laid down, I can reheat with a heat gun in areas that need it. The screen might print the ABS but I'm not too worried about that. You can't see any of the liner from above.