Similar to Bassace, use to play trombone also tuba, so I’m ok with valves. With this in mind I volunteered to play a tuba part in our Swing Band last year at our annual concert. The band arranged the loan of a tuba from a local Brass band, and despite having 5 - 6 weeks to practice my Lip was only just up to the task. I should note I had not played trombone for ten years either but the larger mouthpiece was a killer. I have the same desire to acquire a sousaphone, I did play one in a bass quartet as a teenager, but this last experience has showed me the dedication required to get up to a reasonable standard, but then you need to maintain that level.