Never heard of having to water a foundation, or drip lines for it! And the sand thing, that is surprising for me, but I can kinda relate to it, especially with it being a temporary install that's going to be moved.
Here we don't have clay, if I dig down a few feet anywhere in my yard, I hit ledge rock. My bigger C band dish has been lagged for a year or so now to a big cedar stump and one of my Ku dishes to a smaller one, I was a little dubious of doing this at first, but I didn't want to pour another huge slab of cement right at the time I'd put them up because I'm planning on filling an old foundation on my property with cement and using half of it for a shed and the other half for dishes. Both of those stumps are hard as rock now and haven't split at all, neither dish has moved a bit, go figure. Sand, stumps, if it works, it's good!
Glad to of been some help!