Despite both mine and Parksides best efforts, the LMS van corners didn't look like rolled metal. The two parts met but there was a definite line down each one.
On my workbench, there is a new tube of Deluxe Materials "Perfect Plastic Putty". I don't get on with fillers generally but thought I might as well give this a go.
The results are pretty good. The mixture itself is runnier than I had expected. Despite looking a bit toothpaste, it's smooth and flows well. Squirt out too much as you can even suck it back into the tube. I splodged some onto a bit of the modelling mat and worked it into the crease with a knife blade.
The filler dried quickly - not that surprising as I was using minuscule amounts - and seemed to stay stuck. It doesn't appear to dissolve in plastic glue so there isn't any benefit to brushing Mek-Pak over it. Reading the tube, it suggests water clean up so maybe a wet finger would work.
In my case, a quick rub with a sanding stick looks promising. We'll find out tomorrow when the paint arrives.