No & Yes. Leaf springs are designed not to be lubricated. The internal friction of the spring acts as a form of damping, and reduces the work the shocks have to do. Also, road dust mixes with the lubricant into a sort of grinding paste and knackers the leaves. And the increased travel of the lubricated spring results in high wear at the end of each leaf where it bears on the leaf above, as lubricant is rapidly lost at this point, so the leaf gets thin and eventually breaks. And of course knackers the shocks.
However, having said all that, if ride quality is important to you, and you don't mind replacing the springs and shocks more frequently then Yes, lubricate them with something like a moly grease. You'd need to clean them out say, annually, and regrease, due to the dust/grinding paste thing.
On a trailer, which I assume won't be dragged thru muddy holes, you could do like they did on Rollers n'such, and put gaiters round the springs to keep the dust out, altho this is getting a bit twee for a Landy, in fact if you're a real perfectionist you could even put oil nipples in the gaiters....