>For one, most of them are ugly.
What about putting a vinyl wrap on it then? Or get the kids to spray paint them. Or perhaps if you have a steel shop making decorative steel shapes to glue to the outside.
Perhaps giving the children a sense of investment in the project will make them want to damage them less.
>second problem is it is hard to find large enough ones to house a MR86 with two antenna's like the ANT-27
Electrical enclosures come in all sizes. I guarantee if you go to an electrical wholesaler you'll find one big enough. I'd put everything (antennas, the lot) inside of a single box.
I've used an ABS plastic electrical enclosure on the outside of an ocean-going ship before to house networking equipment. Very harsh environment. Worked fine.