We have the larger Exped 7 deluxe pads...
We have the larger Exped 7 deluxe pads that are 25" wide instead of BA 20" wide. We lash these together with a Thermarest coupler and I wonder can this double wide bag be used just laying it on top of our 2 mattresses without putting them in the sleeves since I doubt they'd fit.
Yes, I just used my BA bag on top of a large air mattress in my back of my truck 2 nights ago. It worked fine.
If you're not going to put the pads inside the sleeping bag sleeve, I'd suggest looking into different sleeping bags (perhaps cheaper ones), like the North Face Dolomite double!