You may have heard the sigh of relief earlier. Most of the grey remained attached to the body!
Masking: I use Tamiya 10mm masking tape for the edges. I chose the BSO for the masking test because of the extra doors and whatnot. The Tamiya tape has a nice sharp edge, and is flexible enough to be pushed down into ridges and edges, and is low tack so - in theory - it doesn't remove paint with it when taken off the work. Once the edges are done, I use normal masking tape to fill in the middle. Other tools are a standard steel rule, a scale rule to let me measure in scale feet and inches rather than strain my brain cell, a scalpel with a sharp 10A blade (and stock of fresh blades) and a propelling pencil.
First up I marked out the panel. I marked a vertical centre point on a couple of window frames at 12mm, and then used my CPL scale rule to give me 1ft 10in either side. I joined the marks up to ensure they were more or less parallel with the body itself.
Richard had agreed the end of the grey panel shouldn't wrap around the body, so I checked sources and worked out by guesstimation the panel stopped about 3in from the door window. The brake end was a bit harder to work out, but it's something just over a foot from the end of the coach. Pencil marks can be removed by the application of a moistened cotton bud; where blue was to cover it I didn't bother cleaning up.
Here you see the Tamiya tape in place. Gentle but firm pressure around the window frames, door strips, and so on, using edge of fingernail and a cocktail stick, ensures as little paint works its way under the tape as possible. My big worry was the grey would pick off when the tape was removed - as indeed it did on the corrosion strips I made from Evergreen strip. (I know they look a bit thick, but they look better in the flesh.)
The gap in the middle was covered by a standard strip of masking tape - which is ironically the exact width of the grey panel. If I could trust the adhesive not to tear off the paint it's masking, I'd probably use it throughout. You'll note I haven't bothered with the corner radii. I find it a bit easier to patch those by brush during the lining process later.
Some time later, after a session in the spray booth, warming the rattle can with my hairdryer (I knew it would come in handy one day!), a brief excursion downstairs because I developed a nosebleed, and about four coats of paint in all, things had dried enough I could risk taking the masking off. It's out of focus because I was so excited. Not really. I think the camera was confused by the shine.
I left things as long as I dared before I decided to take the plunge and remove the sticking plaster. Thankfully, the grey paint appears to be intact. There's quite a lip, though, where the blue met the masking tape, which is a bit disappointing. Hopefully a very careful scrape with a steady hand and sharp blade will clear that. The rest of the tape came away cleanly, apart from one patch by the passenger end door, and those pesky corrosion strips. Some brush painted remedial work will be required.
Some paint inevitably crept under the masking tape. The rattle can process means you have to be a bit closer to the model than really feels comfortable, and if the tape isn't securely settled this sort of thing will happen. Again, I hope a sharp blade, some T-Cut and some careful repair with a brush will sort this out.
The "thin blue line" above the windows will need some more TLC. With luck, the white dividing line will hid the worst excesses. This side is now in the Paint Drying and Hardening Facility (A.K.A. the airing cupboard) to fully harden before further handling
Now to mask up the remaining five sides for a session tomorrow.
Did I mention how much I hate spray painting? It used to be I hated using the airbrush, but I think, on balance, I prefer the finesse of the airbrush over the brute force of the rattle can.