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At f30, the difference in saggita (depth of curve) between a parabola and a sphere is insignificant, so you can make a spherical mirror which is pretty easy.
Now, with a spherical mirror, you don't have to worry about on-axis alignment. Tilt the mirror and it will come to focus away from the main path, and you won't even need a secondary. If you can make a tube rigid enough to hold the componets, then it doesn't matter that it would be impractical to use visually. Many of the early big reflectors used this method.
I'll try to explain this better when I've more time! Must dash ...
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