i'm almost embarrassed to mention this, but the request was for a cheaper alternative.......
3/4" plywood, cut in a circle just bigger than the rim.
jerry can bracket bolted offcenter(on what will be bottom), then bolts thru circle and wheel lug holes(2 worked for me), tightened up against tire.
i did this for many years with my montero and it worked great.
i did this again when i first got suzi, but was not comfortable with the extra weight when i started up-sizing my tires. became concerned about all that extra weight(8.337 lbs/gal.) on that little tailgate.
plus it stuck out farther than i liked(smaller vehicle).
i've mounted it just inside the back on filler side on some stowage contraption i've built.
i can fill it and siphon by just unzipping the window a little.
wish i had some pictures, 'cause i know it sounds hokey, but it really worked well(on my montero) and if i hadn't built the stowage thing, i'd probably still run it.
btw- no bad gas smell having it inside- even when it's sloshing on trails.
i wonder if i should post this?