I bought some wheels for the table I'm building for the egg I haven't bought yet. The wheels came today and look like they'll do quite well.
The tires are 5" diameter urethane, which is recommended in the McMaster catalog for concrete or brick. These have the incredible load capability of 315 pounds per wheel.
These are from www.mcmaster.com. They are called casters.
The swivel one is p/n 2426T54. I got two of these. It doesn't have a brake or lock, if you want one that does, that's the 2426T64.
The fixed one is p/n 2426T74. I bought two of these.
The overall height from ground to the top of the mounting plate is 6.25".
I've got the table-top and it's frame made, and the bottom table and its frame. Haven't got them joined together yet. One thing I'm doing is to cut a hole in the bottom table (bottom shelf?) under the future egg, or more precisely, under the paving stone that the egg will set on, so that if it does get hot there won't be any wood to char. There will be enough supporting structure around the periphery of the paver to support it, though.