I have used giant plastic Christmas ornaments and it worked. I usually silicone a layer of heavy duty aluminum foil to all of my balls first, so I can't say whether the marbles will stay put glued right to the plastic or not...
The only problem I've ever had with them is they are lighter and easier for the neighborhood brats to steal-- or throw in the street and break.
I never put anything in mine, and I left the hole from the hanger open so I could put it on a stake and get it higher....from a distance they look like they are floating (which is probably what attracted the kids in the first place)
I have also used styrofoam balls and had good success with those... but again, I use the foil first. It covers up the base color, so you have something reflective to work with, which enhances the marble color.
HTH

I glued marbles directly on plastic softballs and baseballs and they have held up for years outdoors. So the GEII silicone for windows and doors will hold the marbles to plastic.

Beck what an interesting thing to do, the aluminum foil first I mean. I have some large light bulbs from the building I manage that I painted but I worry the paint will come off and ruin everything. Siliconing Alum foil would be better I think. Could you post a close up of one of yours please?
kathy

I love this question because I am obsessed with bowling balls. I was wondering do you think that it would work to use giant bowl turned upside down to make an animal or something? It seems like you could add marbles or something to the glass surface. I think that I might try it.

Sorry Kathy... I don't have any close-ups handy... I'll see if I can get one.

Honestly, I think GE silicone will stick to anything. So a big bowl is not out of the question. People use marbles on their totems all the time.
Does it have to be glass? I bet you could find a giant plastic bowl that would work too.

I also used the big plastic xmas ornaments from big lots.The first year or so i just put them in the garden,but after the sun faded them,i just glued on the half marbles.Here's a picture of one of them.I didn't add anything to the inside,the weight of the marbles is enough.

{{gwi:148071}}

Kathi

I first pounded a long piece of rebar into the ground. Then slipped an old bird bath base over the rebar.

Ball with one open hole onto the top of the rebar and sitting on the top of the ceramic bird bath base all for stability.

Don't have a photo - raining AGAIN! I think I moved to Seattle in my sleep, house, land, and all!

I've used glass globes, the kind for light fixtures, from the TS to glue marbles on somthing. May have to big of a hole to use in a stand or on a rod for height. Kathy

I use rebar, like Frizzle mentioned, for bowling balls. It gives a floating effect especially in evergreens or other plants that'll grow up and hide the metal bar. If I want it permanent I squish a glob of GEII in one of the holes and set it on the rebar. Helps keep the kiddies from mischief.
I have a bowling ball that sits on an upside down iron plant basket. The metal basket is really too heavy to use for plants, I turned it over and a bowling ball sits nicely on it. Looks kind of spidery, very cool.
I also use metal candle stands and lamp bases. Turn the candle stand upside down and the BB will sit on the feet. The flat candle top which is now the base helps prevent the whole thing from sinking or tipping. The lamp bases I get are from the old 60's and 70's style glass lamps. I use the glass for other projects and the bases for BB, or candles or anything that need a place to sit.
Still haven't unpacked my camera so no pics. Sorry. Hopefully it'll surface soon. Too many boxes........