you can get BDH's from www.upandunder.co.uk tho theyd sold out of some sizes last time i bought some.
BDH's are good because of the different sizes they come in, from ickle baby dinky ones which you can just about get your keys in, through the 1 litre one which is generally use which you can get lunch and a few bits of tat in, upto the biggest ones which you can get stoves etc in. Daren drums are probably a better bet for cameras etc, certainly 2 drums in a tackle sack is the most effective way of carrying largish amounts. The big drums are big enough to fit a sleeping bag in, and the smaller ones are um smaller but just as useful id imagine.
I dont think rocket tubes have much going for them, other than being cheap, they are hard to carry comfortably, other than putting them in a sack, in which case you may aswell use daren drums anyway. think you can get rocket tubes from caving supplies.
Hows your swildons exploring going?