I do have to do some preliminary sanding and test fitting to address any small irregularities in the join area. As Efox does, I also use a few small internal styrene strips to reinforce the hull join, placed in one of the hull pieces with CA glue. But instead of CA, I use 5 minute epoxy for the join itself, as it gives some fine alignment working time before it sets up.

I have tried a number of fillers for the joint seam. Initially I was taping close to the join points on both sides and using Bondo glazing putty. This was followed by sanding when the Bondo dried.

But I recently bought some liquid UV cure resin and a UV curing flashlight flashlight. This allows me to put the resin in the seam, wipe the excess with IPA, then polymerize it with the UV light. After polymerization and inspection, if necessary, you can add another thin layer to build up, or alternatively sand it flush.

The specific products I used with success were: LET'S RESIN UV Resin, 300g Low Viscosity Crystal Clear Hard Type Resin Kit, Quick-Curing & Low Shrinkage and the UV light: Black Light UV Flashlight 365nm Blacklight UV301D. Note the UV light is 365 nm wavelength which works better than the 395 for resin curing. I find 1-2 minutes of UV exposure does the curing. Also keep the resin stored in the dark (it helps that the bottle is black) as sunlight will cure it as well.

Hope this helps.