Benapp

I'm 15 and have been playing atlo sax for 5 years. I really want to march euph in a drum corp, but don't know where to start. I've heard of people doubling trombone and euphonium, so could I learn to play trombone and be just as experienced auditioning on a euph? Or do I just learn to play a concert euph altogether (or get one of those convertible euphs I've seen)? OR, should I just play mellophone since it would be better suited to my prior experience on the alto sax?