Very nice work Chris, been wanting to build one and now it looks like I will follow your style, although I may decide to make it out of plywood for some additional weight as we do get some decent fall winds up here in the Northwest. This way I could also modify your plan and make the base and upper portion seperately allowing it to be attached and removed for storage. thanks for the info and helping to get this guys brain around it!
I used joint compound on my obelisk I made last year - it worked perfectly. Adding sand or mortar mix to the paint also is great for covering any surface blemishes.
As far as anchoring it, I built mine to have a hollow base, and I pound in some wooden stakes and snug the obelisk down over them (spacing them so they press against the sides of the obelisk slightly and you have to really snug it down well) and have had no problems with light to medium winds.
Nice job there, Chris. That is truly an impressive display of overcompensation.
Here is the way I fixed mine incase of high winds.
Here you can see the end of the PVC I cut at an angel to help when driving it into the ground.
Here you can see the stack driven into the ground through the base.
Here you can see the main stack centered in the base of the obelisk.
This is the second piece of the foam (blocks from a cheep fogger box) It is tightly wedged in to the end of the obelisk, for the stack to fit into to help stabilize the upper part in case there was to be winds.
Here is the second foam piece of the inside of the obelisk, it's a larger foam packing from something I or a friend got (LOL). With a hole for the stack to run through; it helps to stabilize the upper part of the obelisk, closer to the base.