I also happen to have this exact same model Huttle, but it is currently in parts awaiting the right time to re-assemble... It can be had for much less than this seller's price, if anyone is interested..
You are in luck! I found the original Huttl catalog from 1912, and it mentions that this particular model sousaphone can double as a vinyl cupola... I'd say buy it now and take mine off my hands to keep as a parts horn for your trailer cupola...
