The company, which manufactures fire surrounds and electric and gas fires from its base in South Shields, Tyne-and-Wear, operates about 60 cars and vans.
It is taking its merchandising staff out of cars and into Vauxhall Vivaro vans fitted with extras such as air-conditioning. They will be used to service contracts with DIY specialist B&Q and other selected national retailers.
Previously the group, which employs about 600 people, had a wide assortment of vehicles on its fleet, including Vauxhall, but has now opted for a single-badge deal with the manufacturer.
Sales and marketing director Richard Appleby said: 'We are a high mileage fleet with many of our cars doing up to 150,000 and even 200,000 miles during their life. That's why we have opted for diesels from Vauxhall, because they are capable of standing up to this sort of punishment.
'We are now ordering Vectra 2.0-litre DTi models for regional sales managers, while those who want a sporty rather than family saloon can opt for one of the new Astra SRi diesels. Our senior managers can choose from models like the Vectra SRi diesel and the new Signum.'
Historically, Be-Modern has outright-purchased its fleet but the new Vauxhall diesels, provided by dealer Sherwoods of Darlington, will be operated over a three-year replacement cycle.