You can buy an "Agri-Tube" from Agricultural Supply Company, http://www.agrisupply.com/category.a...cd2=1268010344
About $ 5 plus shipping.
I just gave away a spare I had around the shop to a KLR rider I met on the Internet; may have another one; if I can find it I will be glad to send it to you; no charge!
The Agri-Tube is about 3-1/4 inches in diameter and approximately 12 inches long. If you mount it low (e.g., on the bash plate), you may want to seal the vent hole with some goop, for waterproofing.
A more elegant mount might be under the left rear side panel, sort of a "faux muffler" orientation.
The welding rod holders (Hobart, Home Depot; Lincoln, Tractor Supply Company) are also about 3-1/4 inches internal diameter, but approximately 15 inches long. These products are waterproof, with a rubber gasket seal. I painted my Lincoln welding rod holder black and mounted it on the Happy Trails bash plate with hose clamps, where it fits between the Happy Trails nerf bar/engine protector rods with clearance to open the cap (I know, I know; a little low and rock-proximate perhaps, but . . . if I break it, I'll buy another!
I wouldn't suggest, "one size fits all," regarding tool tubes--in my view, different individuals have different preferences and requirements. For example, an individual KLRista may prefer and require a 55-gallon drum for his tool tube; I would not presume to dictate he clone my preference and requirement or call his choice a "joke." To do so would seem to me arrogant, egotistical--immaturely narcissistic, and perhaps somewhat megalomaniacal--to each his/her own.
I line my tool tube with a laminated 8-1/2 " X 11" sheet of paper: On one side, "All You Every Really Wanted To Know About The KLR650," a listing of all critical data, diagrams of hub assembly exploded parts diagrams, etc.; and on the other side, a color wiring diagram. (Might get around to E-mailing images of these two reference pages, if requested.)
Will post some pictures when I get a chance.
Otherwise, best wishes on your tool tube, whatever your choice!