Ian, its a good idea in principal, however it really needs to carried out as a stand alone business.
Also regarding floods the companies requiring equipment need lots of it, not just 5-6 dehumidifiers. You have some big players in this market aside from the general hire businesses there is Restoration Express and Corroventa who can call on massive stocks from all over Europe.
One of my colleagues hire bill in Yorkshire last month was 200k.
If you did want to go down this route there should be a lot of gear coming onto the second hand market over the next few months, would be a good time to stock up.