Undersealing - where to get it done?

[HugoFastmann]

I recently had my car on a lift and noticed the underside needs a bit of attention. There's rust showing on what I think is part of the chassis, and it generally needs a good tidy up. Can anyone recommend where to go to get it treated and resealed? I'm in the New Forest but willing to travel within reason to get it done for a decent price.