My dog is almost full grown and she got a new pack

Troy, the top rider doesn't sound a good idea unless you have figured out some new way to keep the pack stable. It could easily become one sided saddle pack.

I have been happy with the way too pricey Ruffwear Palisades, it has taken some serious bushes and rocks with just minor wear. I walk almost always off the trails, so it's really being tested every time we go. Another downside (other than the price) is that it is indeed quite heavy.

I wouldn't want to distribute the weight on their spines like that anyway. I just meant a bag that the bulk of is primarily on top (reduce the bulk w/ultralight gear for dogs), and still supported with a saddle type system. Basically a pack that has no storage on the sides, just a streamlined harness system with protective spectra reinforced covers or something along those lines.

I second the booties comment above. Train your dog to love them. My dogs never have a problem with the snow, but it has saved them from salt and heat. If you're hiking in the sunny desert she will definitely need the foot protection.

"wouldn't want to distribute the weight on their spines like that anyway. I just meant a bag that the bulk of is primarily on top (reduce the bulk w/ultralight gear for dogs), and still supported with a saddle type system."

Tight fitting harness affects the performance and can chafe, so I'm keeping her straps quite loose because of that –> the top pack would easily go sideways, even saddles go unless they are balanced well enough. I would not want to make the center of gravity higher either as we are not avoiding rocky etc. difficult terrains.

If you can reduce the amount of volume needed, a small saddle pack that rides completely at the withers sounds better idea than top loader, but I'm really interested to hear/see the results of your project in any way you end up doing it :)

What else you are planning to lighten up besides the pack itself? And how many days without resupply you are planning to have? Basically all I have left to lighten up is the rain jacket (not sure if more lightweight would be durable enough as the dog isn't exactly careful), collar (could be trimmed a little) and the pack itself. Basically everything else is already left home of as light as possible. Besides rain jacket, collar and the pack she has some dog specific first aid items, small piece of closed cell foam mattress, vegetable oil, dry food, cup, two booties, one water bladder, leash. I have trouble fitting all the food in that big Palisades as I'm moving 7-14 days without resupply on my longer trips. I tried having a smaller pack on the dog for weekend etc. shorter trips, but went back for the big one so that she doesn't have to learn new pack dimensions when we go on those longer trips.