I've for years been using a LowePro beltpack camerabag. Works great. But it's a personal preference of course, see for yourself if it's what you want/need.
LowePro Toploader Pro
Another option (or combine with the Toploader would be the Street&Field series belt with pouches.
The 55-250 might get a bit uncomfortable banging against your leg. Apart from that, I'd not expect trouble. the belts are wide enough to comfortably distribute several kilos of weight. Using the Toploader I can carry a D200 with 70-200 f/2.8 attached and some cleaning kit, spare batteries and CF cards in the front pocket, plus a half liter bottle of water and a monopod around for hours with no problems.
