Despite Mr David Larkin confirming for me the floor of a XVA wagon is an open frame-work, compared to the BDA steel bolster wagon's wooden platform, I am determined to have a means of conveying over-size steel from the manufacturers up north to a small ship-yard south of Atherington East Yard, at Tilling Docks.  The wagon would be conveyed at the head of the goods train 'passing through' my goods yard, so I need not consider load handling in my little general sidings.

What decided me was if I keep the loaded side facing the viewer, the wagon floor would be obscured largely, and if painted black I hope will not be obvious.  So I bought some packs of Evergreen L-shape angle - Nos. 292, 0.080"/2.0 mm. and 294, 0.125"/3.2 mm. and tried to calculate the dimensions of the trestle frame.  Taking Colin J. Marsden's measurements from his 1984 BR and private owner wagons, pp.87-88, of an 8'6" high frame at a 48Deg. angle, I drew a scale diagram of the trestle arrangement:

However, I made the first of several mistakes in thinking the frame propping the 'loading side' was at a right-angle to it.  As one can see from Paul Bartlett's excellent web-site, it is not...

https://paulbartlett.zenfolio.com/brtrestlexva

In blissful ignorance, I made a paper mock-up to balance on the Bachmann wagon, now stripped of its bolsters with a large pair of pliers, and popped a Lima Class 33 diesel in front of it.  The trestle stuck out alarmingly above the loco, so I trimmed off six mm. gradually by eye, this being the final length of the main trestle 'stakes', giving a measurement of 40mm. and the supporting girders of 24mm.  I cut off three sides of the BDA's 'lip', and painted the edges black.  I should have done the whole floor then as well.

Then it was just a case of cutting and shaping ten pairs of girders, and making sure they were the correct orientation.  I glued the bottom of each to a thin strip of plastic square to provide a second 'mount', and worked from the outside to the wagon centre, lest the spacing appear in need of correction - I thought this would give better scope for adjustment.  The gap is 19.5mm.  Propping up the 'load frame' against the wagon's edge, I glued on the supporting girders, scraping paint off the wagon floor to allow the Liquid Poly to adhere, and finally the cross-braces on the back.  The 'diamond' junction plates are 120g./m2 paper, cut to shape.  All was then painted with Humbrol silver, no. 11.

One of many errors is the lack of the three 'steps' either side of the larger central one on the 'support side'.  I assume owing to mis-measurement and/or over-size plastic angle, these will not fit, so am undecided as to whether to ignore them (they will be hidden by the sheet steel load anyway) or cut away the step or girder to fit.

And here is the result in revenue earning service on its way to Tilling Docks, in the yard arrival line.  I intend to fit 0.5mm. painted paper strips over the loads for the plastic strapping.  I assume each sheet was loaded individually, i.e., there was no 'sandwiching' of steel the same size, but could be wrong.  Also there is a hand rail above the steps to add, with painted garden wire.

Lessons for the future: use smaller L-shape angle.  These were the only two on sale at the exhibition, but are too large; there might be smaller sizes made by Evergreen.  Try and get correct measurements (but I do not know how); this might permit the other steps to fit.

I hope this encourages others to have a go.  My results are going to win no prizes, but I like the look, and it might prompt fate to bring out a ready-to-run version.  And my ship-yard can get its steel delivery.