Thanks all. Phil's caps are for the ends - I may need those in future, but not at the moment. CarlF's feet require fixing - my trainer doesn't have fittings for that, but could be worth trying whether I can tap it I suppose. The saddle feet that I've seen for smaller tubes wrap around the tube more and would hopefully stay in place anyway. Lissotriton's idea may work perhaps - and I may need to try it if I can't find anything else!