For a travelling show it makes reasonable sense to use a largish case to (a) contain the organ works & (b) serve as a stage/backdrop. Assuming side > rear, the side might seem the preferred option, but then you’ve got the visual distraction of the rest of the bike. One way of increasing the rear width is to use hinged doors on the back to get a triptych. Here are a couple of mockups of the triptych-ised rear elevations using a Cycles Maximus soft-top cargo bike with the top structure modified to give an extra 45cm or so vertical reach. I like the Mortier one:
At least the look, and possibly the functionality, of the side doors would obviously need to be reasonably flexible.
Here for additional amusement & extra refs is the OED entry for triptych:
1731GALE in Phil. Trans. XXXVII. 161 The Diptychs and Triptychs that were covered with Wax, served only for common Occurrences. 1885E. M. THOMPSON in Encycl. Brit. XVIII. 154/1 These triptychs then were libelli of three tablets of wood, cleft from one piece and fastened together, like the leaves of a book, by strings passed through two holes pierced near the edge. Mod. Advt., Confirmation Triptych. A small-folding Triptych Certificate Card.
2. A picture or carving (or set of three such) in three compartments side by side, the lateral ones being usually subordinate, and hinged so as to fold over the central one; chiefly used as an altar-piece.[
1848A. JAMESON Sacr. & Leg. Art (1850) 227 In a tabernacle or triptica by Niccolo Frumenti, the central compartment represents the raising of Lazarus.] 1849CURZON Visits Monast. 366 The most valuable reliquary of St. Laura is a kind of triptic. 1852A. JAMESON Leg. Madonna Introd. (1857) 53 A Triptych is an altar-piece in three parts. 1896Church Times 14 Aug. 154 There is no east window, but above the altar is an exquisite triptych. 1925R. A. STREATFEILD Opera (ed. 5) xiii. 304 Puccini’s last work is a so-called ‘triptych’, consisting of three one-act operas. 1928Grove’s Dict. Mus. (ed. 3) IV. 283/2 In this triptych the composer’s technique is more elaborate than in ‘Butterfly’. 1959Listener 31 Dec. 1176/3 Any music that makes a strong visual suggestion like the Debussy orchestral triptychs. 1976New Yorker 1 Mar. 90/1 This season, the triptych has been reassembled: a new ‘Tabarro’ and ‘Suor Angelica’ join the 1974 staging of ‘Gianni Schicchi’. 1976Gramophone Sept. 424/2 Ormandy’s version (which offers 24 minutes’ extra music in the form of Feste romane, the still more luridly coloured third leaf of the triptych) will do very nicely. 1976Oxf. Compan. Film 494/2 After the first presentation it [sc. Napoléon] was released in a truncated version from which the triptych sequences had been removed: Gance, disappointed by the poor reception, destroyed much of the original footage, including some of the triptych. 1980Times 5 Dec. 11/5 The great triptych – Gancecalled it Polyvision – inno respect falls short… From the breath-catching moment when the screen is suddenly multiplied to reveal a great panorama of the Grand Army on the Alps, Gance’s use of the triptych is light years in advance of anything three-projector Cinerama ever achieved. Ibid., Sometimes the triptych image is a continuous panorama; sometimes it is split into different images. There are superimpositions and mirror images, the whole orchestrated with passion. 1908Westm. Gaz. 21 Jan. 4/2 The triptyque, or special card which opens the doors to half-a-dozen countries, and relieves its holder of much bewildering formula when touring abroad. 1909Daily Chron. 9 July 8/3 The adoption of the triptyque, or international passport, for balloons and aeroplanes such as is now in use for motor-cars.