Yeah I did think of that. My concern would be it eventually leaking, or giving way entirely. You know yourself, it'd do it at the worst possible moment. I may use a 5 gallon drum with a tap on it, always be a bit sloshing about in the bottom, but no harm done.
Below is the basic idea I've had so far, some good points brought up on this thread though! Filling the roller pipe with foam is a good one.
My thinking has gotten this far:
Two mountain bike wheels on a frame. A (for arguments sake) 6 foot long pipe with a series of paint rollers on it...
Apologies if dragging up an old thread is bad form on this forum. but, I'm really interested in this thread and was wondering if there were any more updates/info/photos? I'd like to make my own weed licker/wiper, though I'd design a lightweight more compact one that I could push about myself...