For the TOMA layout project ...

Sheet Metal

I used sheet metal...

http://model-railroad-hobbyist.com/node/25230

The edges naturally lie very flat against the wall:

Using styrene instead of vinyl

Thanks, Joe. That stuff looks very interesting. Since I would be looking at using it for only the coves, not the main backdrop (planning to use tempered hardboard), would the rest of the process as given in the article apply? That is, using cove base adhesive to affix the styrene to the perpendicular panels of hardboard and using tape/mud to smooth the transition from the styrene to the hardboard? Also, since this styrene is 15 mils -- the same as the vinyl flashing -- would it be reasonable to just using a single ply? Not sure if the styrene is as rugged as the vinyl for a given thickness.

One last question, I tried plugging in a test purchase to see the shipping costs. Near as I can tell, those 26"x60" sheets fall into category C which leads to a shipping cost of $116, even for a single sheet. Was your cost estimate based on having them cut the sheets down to get to category B (which drops the shipping cost to $30).

Cheers,

Vince

"I also thought about vinyl

  What are you planning to do the straight runs with? The extra thickness of vinyl flooring might be a good thing if your straight section material is thicker?  I used masonite for the bulk of my backdrop but used more flexible thin plywood for the coved corners so the thickness matched pretty well.. Vinyl flooring is very flexible, flooring installers cove corners with it smaller than what one would use on a layout backdrop......DaveB 

Planning to use hardboard for straight runs

I am planning to use hardboard for the straight runs. The thing that sounded so appealing about the vinyl flashing was that (at least if i read the article correctly) the coved corner was applied directly on top of the hardboard. So, no need to measure and cut very accurately to make sure that the ends of the curved piece butt up perfectly against the ends of the straight pieces. That is, I could be somewhat sloppy with the straight runs as they run roughly to the end of the wall into the corner (minus a few inches, if desired, as the cove would cover it) and the curved piece would hide all of that as it would be applied on top. With something like a much thicker vinyl flooring, I assume I would have to pay more attention to the cutting and lining up of everything. Either that or apply it on top as well and just do a lot more feathering with the mud/tape.

Maybe I am just more afraid of it than I need to be ...

They send it as rolls

They send it as rolls (non-sheet packing) in a small regular box, so category A shipping: $21 for 20 rolls (50 feet laminated). See the product note: This item will be rolled for shipment by UPS or FedEx for lowest cost shipping rate.

You could also use it unlaminated if you wanted thinner material. Vinyl will be more flexible but otherwise styrene is very similar - and styrene holds paint well.

 "With something like a much

I set my thin plywood corner pieces flush with the masonite straight sections to minimize feathering. I cut 12 inch radius plywood forms for top and bottom then installed the straight masonite sections then measured and cut the plywood curve pieces and snapped them into the corner. Staples into the plywood curved form held the corner at top and bottom and brad nails into the splice backer at the joints secure everything( the plywood is held  in place by the ends against the masonite so little strain on the fasteners) Here's a couple of photos showing the curved plywood top and bottom forms and the corner backdrop in place and smoothed up....DaveB 

AMAZON has 18" rolls x 50'

Amazon has this brand - 18" x 50'

Could not find thickness listed anywhere but the 50' roll weighs less than 6 lbs, so guess it would be pretty thin.

https://www.amazon.com/Resysvn18-50-White-Vinyl-Flashing/dp/B01BCIPJW2/ref=sr_1_6?ie=UTF8&qid=1506392414&sr=8-6&keywords=vinyl+flashing