plus a similar sized nice long bit of mdf then fix it with double sided tape you'll have a massive sanding block. That way you can use the surrounding flat surfaces to do the work.
In classic fashion I'm doing everything backwards. Stove has now been installed, going to have a go at patching it myself and like the idea of sand paper on MDF as looks like it would work nicely with the flat edge on the inside of the curve.
If you get one of these sanding rolls
plus a similar sized nice long bit of mdf then fix it with double sided tape you'll have a massive sanding block. That way you can use the surrounding flat surfaces to do the work.