Mercury lamps are very bright and delicate/expensive a serious moth-ers choice
I have made one from a heavy duty folding crate(B&Q)a strip of ply that slides
firmly through the handles and carries a bulkhead lamp fitting and an eco-lamp
(there is even a dawn to dusk switching version)
The whole lot folds reasonably flat for storage,there are plans here for another type;
http://www.angleps.btinternet.co.uk/moth_guid.pdf