[Wavytone]

The Mersenne is just a pair of confocal parabolic mirrors - concave primary, convex secondary - producing an afocal beam coming through the primary, followed by a smaller telescope some distance behind the primary mrror - a fast lens with an aperture large enough to collect the beam. If the Mersenne primary was say 30 cm aperture I'd expect a 60-80 mm aperture will be adequate for the refractor.

The Mersenne is aplanatic, anastigmatic and achromatic, it contributes magnification without producing an image. In a practical implementation the abberations from the small telescope at the end are what will be evident in the final image.

If the refractor was f/5 and the Mersenne magnification x3, the result is f/15.

You can definitely use two or more folding flats (or star diagonals) to bend this beam where you want it.

The only downside is the number of surfaces involved and the losses resulting, but it could be viable...

As for making the pair of mirrors, it is no harder than making a classical cassegrain provided the optician has a way of star testing the complete system on an optical bench.