While I agree that the cover is the worst part about most of these traditional RTT's I have never had any issues getting all the tent material to fit. I spoke with CVT once about the difference in the Pioneer and Summit covers and the Pioneer cover has bump-outs (for lack of a better term) for the ladder(s). That's why they look so much tighter than my Summit Series which is just one large box shape.
Here's a post I made in the 'keeping the annex attached' thread for how I fold mine up. This is with (2) 32" wide very thick winter sleeping bags zipped together inside (jack and jill style). I've always just folded my extended vestibule material over the top of the tent and never tuck it inside since it's so heavy.
Hahahahaha. Yeah, either mine is a misbuild or the Shasta cover is way different. I can barely get the cover on with nothing in the tent. To put 2 pillows and 1 backpacking sleeping bag in there requires a ratchet strap to compress the tent to get it close to parrelel in the closed position and the cover barely goes on. I have one sleeping bag like you mentioned and I can't even get the cover on with it inside. There is no way in hell I could ever put the annex on top of the tent. This is in warm weather. I also use a strap around the perimeter to avoid 20 minutes of trying to tuck and poke the sides in enough to zip the thing up. Plus the front side by the cab of the truck I can't reach so a strap is really the only way to push it in.
Your vestibule is more rectangular which might lend itself to flipping over the top. Mine is square so the sides I think won't really let me. But I will try it.
I like the durability and solidness of the summit material but trying to bet my particular tent closed is a nightmare.
I'm becoming convinced my tent or cover is out of spec. In freezing weather it is almost impossible to pack up.
It really ruins my experience and defeats the purpose of having a ready made bed when I have to schlep a lot of my sleeping stuff out of the tent and find watertight storage in my truck bed.
Looking how neat and organized your write up is and how awesome and functional it would be to pack like that and knowing how easy that cover must go in with nothing on top to even be able to attempt the extra stuff is literally making me ill.