I am moving along on the construction of my SWB. The frame is
brazed/welded up and I only need to braze on the brake mounts before I
paint!

However, I've noticed that nowhere in the plans is there any mention
of capping the derailleur stem tube nor the back end of the main tube.
I live in Seattle and I expect and plan to do a fair amount of riding
in the rain. I would imagine that water getting into these tubes
would be ... bad.

I'm thinking of cutting some circular caps out of the same steel plate
I made the dropouts from, then brazing them to the inside of the
tubes. However, I thought I'd ask: can anyone think of any reason why
I *shouldn't* close up these tubes?