Interesting 'extras' produced by this company - Stedall in Bristol .
I am currently checking out their 50cmx50cm alloy frame roof ventillation/light window ( fits between the main roof struts on a hightop and isn't too pricey) and their side steps https://stedall.co.uk/vehicle-access-made-easy-2/
The manual step mechanism looks a bit 'clunky' but might be handy on a commercial vehicle