TURTLE-- Already planning on that but want something a little more portable.
Another way to do it is go with an outboard motor gas can. They have to be built better than a cheap gas can because they have to be air tight for boating regs. They are also big on the base so they won't tip over like a gerry can will. You can also rig them up to auto fill with the squeese bulb.
If you are creative, Rotopax has some interesting ways to mount fuel containers, such as on the top of the MH or toad, on the back of the MH. Their stuff is pricy, but you get what you pay for, and the containers can be mounted at almost any angle (horizontally, vertically, etc.) and you can get a locking T-handle to prevent the gas cans from waltzing off.
If the toad has a roof rack, then this makes the job a lot easier (assuming it isn't any trouble to reach up there.) You can stack the Rotopax containers, so you can carry multiple ones on top (watch the weight limit on the roof though.)
There is the option of adding a rear hitch receiver, and a receiver cargo rack, but that does add length, might scrape the ground, and might get hit by people behind (who are expecting a MH and toad, not a MH, toad, and rack.)